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动物学报  49 ( 3) :370~379 , 2003 A ct a Zoologica S i nica        

Spermatogenesis , spermiogenesis and spermatozoon in the cestode ( Moniezia expa nsa ) ( Cyclophyllidea , Anoplocephalidae) 3 L I Hai2 Yun ①33  Gerard P. BRENNAN ②  David W. HAL TON ② ( ① A ni m al Science College , Sout h Chi na A gricult ural U niversity , Guangz hou  510642 , Chi na) ( ② Medical Biology Cent re , The Q ueen ’s U niversity of Belf ast , Belf ast B T 9 7 BL , U K)

Abstract  The processes of spermatogenesis and spermiogenesis , and t he fine structure of t he spermatozoon in t he cyclo2 p hyllidean cestode Moniez ia ex pansa , were examined using a combination of light , scanning and transmission electron mi2 croscopy. Primary spermatogonia were found mainly in t he testes of young proglottids. Primary spermatogonia divided in2 to two secondary spermatogonia and t hereafter incomplete divisions gave rise to 16 primary spermatocytes in t he form of a rosette , wit h all cells sharing a common cytoplasm. Synaptonemal complexes appeared in t he nucleus of t he primary sper2 matocyte and mark t he meiotic prop hase , t he first mature division leading to 32 secondary spermatocytes. Successive sec2 ond mature divisions gave rise to a rosette of 64 spermatids. Spermiogenesis began wit h t he formation of a differentiation zone in t he form of a conical2shaped projection of cytoplasm delimited by a ring of arched membrane. Wit hin t his area , t here were two centrioles and associated spiral rootlets. During spermiogenesis , only one of t he centrioles developed an ax2 oneme t hat grew directly into t he cytoplasmic extension ; t he ot her centriole was aborted. The nucleus elongated and moved into t he cytoplasmic extension. After transformation , t he spermatozoa left t he cytop hore and mature. Any remain2 ing rosettes of spermatids de2differentiated to form an electron2dense residual body. The mature spermatozoon of Moniez ia was filiform , tapered at bot h ends and lacked mitochondria. In cross sections , t he spermatozoon had : ( 1) a plasma mem2 brane and crested2like body ; ( 2) 1 - 4 fields of microtubules beneat h t he plasma membrane. The number of cortical mi2 crotubules varied in different regions ; ( 3) electron2dense granular material in t he cytoplasm ; ( 4) an irregular2shaped nu2 cleus ; ( 5) an axoneme of“9 + 1”pattern lacking a peri2axonemal sheat h. Based on longitudinal sections of t he spermato2 zoon , five regions could be distinguished. Its anterior extremity exhibited an apical cone of electron2dense material , and two crested2like bodies. The cortical microtubles varied in lengt h and follow a 25 - 45 degree helicoidal pat h along t heir lengt hs. They were arranged in 1 - 4 fields in different regions. The axoneme did not reach t he very end of t he anterior extremity ; near t he posterior extremity it formed a free flagellum. The nucleus was arranged in an elongated , compact and irregular cord t hat spirals around t he axoneme. Numerous small electron2dense granules occupied t he cytoplasm in re2 gions Ⅲ to Ⅴ. To t he best of our knowledge , t his is t he first report of a free flagellum in t he spermatozoon of a cestode [ A cta Zoologica S i nica 49 ( 3) : 370 - 379 , 2003 ] . Key words  Cestode ( Moniez ia ex pansa) , Spermatogenesis , Spermiogenesis , Spermatozoon , Ultrastructure

扩张莫尼茨绦虫 ( 圆叶目 : 裸头科) 精细胞分化 、 精子形成及精子形态 3 李海云 ①33  Gerard P. BRENNAN ②  David W. HAL TON ② ( ①华南农业大学动物科技学院 , 广州 510642) ( ②Medical Biology Centre , The Queen’ s University of Belfast , Belfast B T9 7BL , U K)

  Received 28 J une , 2002 , revised 15 Oct . 2002   3 This research was funded by grants from t he National Natural Science Foundation of China (No. 39900109) , t he Natural Science Foundation of Guang Dong (No. 980128) and by t he School of Biology and Biochemistry , Medical Biology Centre , Queen’ s University Belfast , U K.

33 Corresponding aut hor.  E2mail : hyli @scau. edu. cn   Brief introduction to the f irst author : Female ,Ph. D. Research interests : biology of parasites.   ν 2003 动物学报 A cta Zoologica S i nica

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Li Hai2 Yun et al . : Spermatogenesis , spermiogenesis and spermatozoon in t he cestode

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摘  要  本项研究应用光学显微镜 、扫描和透射电子显微镜 , 观察了扩张莫尼茨绦虫的精细胞分化 、精子形成 全过程及精子的精细结构 。扩张莫尼茨绦虫的精细胞分化过程为 : 1) 初级精原细胞主要发生于幼节的睾丸滤泡 中 ; 2) 次级精原细胞发生不完全分裂形成 16 个细胞一簇的初级精母细胞群 , 以共同的中央细胞质相连 ; 3 ) 初 级精母细胞的特征为细胞核中出现联会复合体结构 ; 4 ) 紧接着的第二次成熟分裂 , 产生 64 个由中央细胞质相 连的细胞核较小的精细胞 。精子形成始于精细胞中分化区的形成 , 成熟精子缺乏线粒体 , 具有质膜和冠状体 、1 ~4 个领域排布的质膜下皮层微管 , 细胞质中存在电子致密的颗粒状物质 , 具一个不规则形态的细胞核 , 具有 “9 + 1”类型的轴丝构造 , 缺乏轴丝周围鞘 。从精子的纵切面上可将精子区分为 5 个区段 ( Ⅰ~ Ⅴ区 ) 。在精子 形成过程中 , 中心粒基部出现螺旋形小根结构在寄生虫中为首次报导 ; 成熟精子具有游离鞭毛 , 在绦虫中为首 次发现 [ 动物学报 49 ( 3) : 370~379 , 2003 ] 。 关键词  扩张莫尼茨绦虫  精细胞分化  精子形成  精子  精细结构

    M oniez ia ex pansa ( Rudolp hi , 1810 ) has a worldwide dist ribution. It is one of t he largest tape2

ice2cold 4 % glutaraldehyde in cacodylate buffer con2

worms known , measuring up to 6 m in lengt h and

taining 3 % ( w/ v) sucrose p H 714 for 4 h , buffer2

116 cm in widt h , and occurs predominantly in t he in2 testine of sheep , goat s , cattle ( mainly in lambs ,

washed and dehydrated for embedment in JB4 resin. Following polymerisation , sections ( 2 - 4 μm in

kids , calves) and ot her ruminant s. Rat her t han caus2 ing direct stock losses , infection wit h t he worm

t hickness) were cut and air2dried on slides for stain2 ing wit h toluidine blue or periodic acid2Schiff ( PAS) .

brings about indirect losses , such as reduced weight

Ot her samples ( n > 20) were fixed overnight in a 3∶ 1

gain , host malnut rition and anaemia , blockage , di2

mixt ure of 4 % glutaraldehyde and 015 % aqueous os2

gestive dist urbance , and sometimes diarrhoea or con2 stipation. It is especially harmf ul to young animals

mium tet roxide for examination by scanning elect ron microscopy ( SEM ) . Following fixation and several

under 9 mont hs of age.

changes in cacodylate buffer2wash , specimens were

20 ) for light microscopic examination were fixed in

Fecundity is an important characteristic of para2

dehydrated t hrough a graded acetone series , critical2

sites and t his is especially t rue of M oniez ia ex pansa.

point dried in CO2 using an Emscope CPD 750 criti2

The worm has two set s of reproductive organs in each

cal2point dryer and mounted on aluminium st ubs ,

proglottid , and t he mechanism of reproduction is bot h

coated wit h gold/ palladium in an Emitech K550 sput2

of biological interest and of economic significance.

ter2coater and viewed on a J EOL J SM235CF scanning

For t his reason , we conducted an ult rast ruct ural matozoon in M oniez ia ex pansa to provide baseline in2

elect ron microscope at 10 - 15 kV . Finally , samples ( n > 10 ) for t ransmission elect ron microscopy ( TEM) were fixed immediately as for JB4 for 4 - 5

formation on reproductive develop ment in t his worm.

h , followed by two 015 h washes in cacodylate buffer

We hope t hat t he result s will give a better insight into

and stored for 24 h in cacodylate buffer prior to post2

t he worm’s reproductive st rategy and t hus be of value

fixation in 1 % aqueous osmium tet roxide for 2 h.

in population cont rol st udies , as well as provide data

Specimens were t hen dehydrated t hrough an et hanol

st udy of spermatogenesis , spermiogenesis and sper2

of p hylogenetic value.

series and orientated appropriately prior to embed2

1  Materials and met hods

ment in Epon 812 resin. Ult rat hin sections were cut

Adult specimens of M oniez ia ex pansa were col2

and collected on uncoated 2002mesh copper grids , stained wit h alcoholic uranyl acetate ( 15 min ) and

lected f rom t he intestines of sheep slaughtered at La2

aqueous lead cit rate ( 8 min ) , and examined using a

gan abattoir , near Belfast , U K. Worms were placed

J EOL 1002CX elect ron microscope operated at 100

in warm 019 % p hysiological saline and maintained at

kV .

35 - 37 ℃ in a vacuum flask for t ransport to t he labo2 ratory. There t hey were quickly cut into small ( ap2

2  Result s

proximately 015 cm long ) pieces. Specimens ( n >

211  Spermatogenesis and spermiogenesis

372

动   物   学   报

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Primary spermatogonia were most evident in t he

t ure division. Occasionally , two cent rioles arranged at

testes of young proglottids and located at t he perip h2

right angles were found in t he perinuclear cytoplasm.

ery of t he testes. As t he proglottid developed , prima2

Large numbers of

ry spermatogonia divided twice forming secondary and

unattached ribosomes and rough endoplasmic reticu2

tertiary spermatogonia. Tertiary spermatogonia t hen

lum were found t hroughout t he cytoplasm. Element s

underwent incomplete division resulting in an 82celled

of a Golgi apparat us were found at t his stage.

mitochondria , polyribosomes ,

rosette of primary spermatocytes joined at t heir bases by common cytoplasm in t he form of t he cytop hore. The eight primary spermatocytes underwent a syn2 chronous division to form a rosette of 16 secondary spermatocytes. Thirty two spermatids arose by a sec2 ond mat ure division of secondary spermatocytes and t hese subsequently t ransformed into t hread2shaped mat ure spermatozoa. Event ually , t he spermatozoa be2 came detached , leaving t he remaining common cyto2 plasm as a residual body. All of t he gradual t ransi2 tional changes in fine st ruct ure which occured during spermatogenesis in M oniez ia ex pansa were briefly summarized as follows. 21111  Primary spermatogonia ( Fig. 1 : 1 and Plate

Ⅰ: 2 )  Primary spermatogonia were morp hologi2 cally characterised by t heir somewhat irregular shape , and were located at t he perip hery of t he testes. The nucleus was large and generally round , wit h a few clumps of heterochromatin ; t he nucleoplasm was granular. The cytoplasm was relative elect ron2dense and largely occupied by numerous small ovoid mito2

Fig. 1  Diagrammatic interpretation of spermatogenesis and spermiogenesis in the cestode ( Moniezia expa nsa ) 1. Primary spermatogonia  2. Secondary spermatogonia  3. Pri2

chondria , scattered populations of polyribosomes and

mary spermatocyte  4. Secondary spermatocyte  5. Spermatid  6.

ribosomes and linear arrays of sparse endoplasmic

Onset of spermiogenesis showing a differentiation zone , note spiral

reticulum. No evidence of a Golgi apparat us was

rootlets (arrow)  7. Spermiogenesis as seen by light microscopy ,

found at t his stage. 21112  Secondary spermatogonia   ( Fig. 1 : 2 and Plate Ⅰ: 2 )   Secondary spermatogonia were dis2 t ributed wit hin t he outer layer of primary spermato2 gonia. Most of t hem were sp herical or elliptical in

showing large numbers of t hread2shaped spermatozoa forming from a rosette of spermatids N : Nucleus  n : Nucleolus  m : Mitochondrion  S : Synaptonemal complex  G: Golgi complex  GER : Granular endoplasmic reticulum c : Centriole  R s : Rosette  Am : Arched membrane

was similar to t hat of primary spermatogonia but less

21114   Secondary spermatocytes ( Fig. 1 : 4 and Plate Ⅰ: 1 , 5 )  The body of t he secondary sper2

elect ron2dense.

matocyte was distinguished by t he arrangement of it s

21113  Primary spermatocytes ( Fig. 1 : 3 and Plate Ⅰ: 1 , 3 , 4)  Primary spermatocytes were morp ho2

ranged just beneat h t he plasma membrane and perinu2

shape , wit h large round nuclei. Their fine st ruct ure

logically irregular wit h a round nucleus and could be i2

mitochondria in two fields : cortical mitochondria , ar2

dentified by t he presence of a nuclear synaptonemal

clear mitochondria close to t he nuclear envelope. 21115  Spermatids ( Fig. 1 : 5 and Plate Ⅰ: 1 , 6 )

complex , indicating pairing of homologous chromo2

Spermatids were located at t he side of t he rosette wit h

somes during t he meiotic prop hase of t heir first ma2

t heir cytoplasm connected to t he common cytop hore.

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Li Hai2 Yun et al . : Spermatogenesis , spermiogenesis and spermatozoon in t he cestode

373

toplasm. The Golgi apparat us was well developed at

①) , roughly 200 nm - 450 nm in widt h , corre2 sponded to t he anterior ext remity of t he spermato2 zoon . It was capped by an apical cone of elect ron2 dense material wit h an approximate widt h of 250 nm and a lengt h of about 300 nm. This region presented

t his stage , wit h membraneous stacks and associated

two helicoidal crested2like bodies associated wit h t he

vesicles.

subjacent microt ubules. The t hickness of t he crested2

21116  Spermiogenesis ( Fig. 1 : 6 , 7 and Plate Ⅱ: 7 - 10 )  Spermiogenesis began in each spermatid

like bodies decreased gradually towards t he beginning of region Ⅱ. An axoneme of t he“9 + 1”pattern was

wit h t he formation of a differentiation zone , limited

located cent rally but did not reach t he very anterior

by sub2membranous cortical microt ubules , in t he

end. It lacked a peri2axonemal sheat h and was sur2

form of a conical2shaped projection of cytoplasm bor2

rounded by a t hin layer of slightly elect ron2dense cy2

dered by a ring of arched membrane. In t he conical

toplasm. The cortical microt ubules spiralled at an an2

area , t here were two cent rioles and associated spiral

gle of about 25 - 45 degrees to t he longit udinal axis of

rootlet s; t he two cent rioles were at right angles to

t he spermatozoon. In longit udinal sections , and in

each ot her. During spermiogenesis , only one of t he

t he surface layers of t he spermatozoon , cortical micro2

cent rioles develops an axoneme. This grew directly

t ubules formed a discontinuous layer of elect ron2dense

into t he cytoplasmic extension ; t he ot her cent riole

appearance. In cross sections , t hey were arranged in

was aborted. The cortical microt ubules rapidly elon2

They had small , round nuclei located in t he cent re of t he cell bodies , wit h large numbers of mitochondria , polyribosomes , unattached ribosomes and rough en2 doplasmic reticulum dist ributed t hroughout t heir cy2

gated and spiralised. The nucleus underwent consid2

two fields associated wit h t he crest2like bodies. Region Ⅱ ( Fig. 2 : Ⅱ, ②; Plate Ⅱ: 11 , 13 -

erable elongation , became filiform , and moved into

16 : ②) was f rom 450 - 500 nm in breadt h , it lacked

t he cytoplasmic extension. Later , as t he nucleus con2

crest2like bodies but exhibited helically2arranged cor2

tinued it s migration , two crest2like bodies appeared in

tical microt ubules , seen as a continuous layer of dense

t he anterior part of t he spermatid. Concurrently ,

submembranous material , and whose numbers were

elect ron2dense granules condensed and progressively

increased. The axoneme was seated in t he cent ral

dispersed towards t he distal areas of t he spermatid.

area and was surrounded by a fine layer of elect ron2lu2

Towards t he end of spermiogenesis , amorp hous elec2

cent cytoplasm.

t ron2dense material condensesd at t he anterior ex2 origin of t he apical cone of elect ron2dense material

  Region Ⅲ ( Fig. 2 : Ⅲ, ③; Plate Ⅱ: 12 , 13 , 15 : ③) was f rom 500 - 700 nm in widt h. It was characterised by t he presence of an axoneme en2

presented in t he anterior end of t he mat ure spermato2

veloped by a t hick layer of elect ron2lucent cytoplasm

zoon. Finally , t he ring of arched membrane narrowed

wit hin which t here were numerous granules of elec2

and const ricted such t hat t he mat ure spermatozoon

t ron2dense material resembling in appearance granules

t remity of t he spermatozoon. This was probably t he

became detached f rom t he residual cytoplasm. The

of glycogen. The cytoplasm was surrounded by spi2

latter remained and condensed as an elect ron2dense

raled cortical microt ubules , as in region Ⅰ. The

residual body.

number of cortical microt ubules were at a maximum

212  Fine structure of the spermatozoon

at t his site. No nucleus was apparent in t his region. Region Ⅳ ( Fig. 2 : Ⅳ, ④; Plate Ⅱ: 11 - 14 ,

Examination of an individual spermatozoon f rom anterior to posterior portion revealed five distinct re2 gions ( Ⅰto Ⅴ) . While no marked topograp hical dis2

16 : ④) was f rom 700 - 500 nm in widt h. This re2

continuities in morp hology between t he five regions

which was coiled in an irregular spiral around t he cen2

were evident using SEM , t hey exhibited distinctive

t ral axoneme. It appeared as a compact cord and

ult rast ruct ural feat ures when viewed by TEM. Region Ⅰ ( Fig. 2 : Ⅰ, ①; Plate Ⅱ: 9 , 11 :

showed a different morp hology in diverse cross2sec2

gion was characterized by t he presence of a nucleus ,

tions. Numerous elect ron2dense granules were dis2

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during spermatogonial division in parasitic platy2 helmint hs is still unknown ( Rybicka , 1966 ) . The first detailed st udy on spermatogenesis in M oniez ia was conduced by Child ealy t his cent ury using light microscopy. In t his original st udy , spermatogonial division was interpreted as amitosis. Later , Young claimed t hat spermatogonial division involved“chro2 midial ext rusion ”. The 1960 ’s wit nessed t he int ro2 duction and use of t he elect ron microscope in t he field of parasitology , including ult rast ruct ural st udies of spermatogenesis in cestodes. However , despite t his advance in investigative technology t he nat ure of cell division in t he spermatogonia of cestodes remains un2 clear.

Pashchenko once claimed t hat

in

Tae2

niarhy nchus sagi nat us , spermatogonia divide by bot h

mitosis and amitosis ( Rybicka , 1966 ) . Nonet he2 less , many workers ( including Tian et al . , 1998a , Fig. 2  Schematic of a mature spermatozoon of Moniezia expa nsa , showing f ive distinct regions

( Ⅰ2 Ⅴ or ①2 ⑤) from anterior to posterior

b ; Mahendrasingam et al . , 1989 ; Rosario , 1964 ; Xylander , 1989 ) mentioned t hat mitosis occurs , al2 t hough no clear images of t he mitotic p hases have

Ac : Apical cone  Ax : Axoneme  cb : Crested2like body  cm : Cor2

been presented. We did not find eit her mitosis or

tical microtubules  G: Granules of glycogen  pm : Plasma mem2

amitosis p hases. The main reason for t his may be t hat

brane  N : Nucleus  F : Flagellum  Pse : Posterior spermatozoon

t he dividing stage is very brief compared wit h t he in2

extremity

terp hase. From a t heoretical point of view , bot h mi2

t ributed around t he axoneme in t he elect ron2lucent cytoplasm. Out side t he cytoplasm , t here was still a layer of spiraled cortical microt ubules , which were ar2 ranged in 2 - 4 fields. Region Ⅴ ( Fig. 2 : Ⅴ, ⑤; Plate Ⅱ: 13 , 14 , 16 : ⑤) was less t han 500 nm in widt h. It corre2 sponded to t he posterior end of t he spermatozoon. In t his region t he axoneme appeared at t he side of t he

tosis or amitosis could occur in cestodes. Mitosis , as previously mentioned , has been recorded in spermato2 gonial division in many animals , especially in verte2 brates and insect s. Cestodes represent part of a large p hylum of lower Bilateria invertebrates , and as such it is possible t hat mitosis takes place in t heir sper2 matoginal divisions. Amitosis occurs mainly in proto2 zoans and has also been found to take place in t he for2 mation of plant microspores ( Han , 2001) . The sper2

spermatozoon in some cross sections , while in ot her

matogenic stage in animal ontogenesis is roughly e2

sections no axonemes could be seen. From all t hese

quivalent to t he protozoan stage in animal p hylogene2

observations , it could be deduced t hat t he axoneme

sis. It is possible , t herefore , t hat amitosis could also

grew out of t he spermatozoon body and formed a f ree

occur in t he spermatogonial divisions of cestodes. To

flagellum.

confirm t his , f urt her detailed st udies are needed.

3  Discussion

312  Spermiogenesis J ustine ( 1998 ) summarized most literat ures on

311  Spermatogenesis

spermiogenesis in

cestodes

and

described

four

It is widely believed t hat mitosis occurs during

spermiogenesis types. Type Ⅰ, wit h two flagella ;

t he process of spermatogonial division in vertebrates

during spermiogenesis t here is flagellar rotation and

and insect s. Whet her mitosis or amitosis takes place

proximo2distal f usion ; occurring in some cestodes of

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Li Hai2 Yun et al . : Spermatogenesis , spermiogenesis and spermatozoon in t he cestode

t he orders : Tet rap hyllidea , Onchobot hriidea , Proteo2 cep halidea , Trypanorhyncha and Pseudop hyllidea ; Type Ⅱ, wit h only one flagellum ; spermiogenesis ac2 companied by flagellar rotation and proximo2distal f u2 sion ; found in some cestodes of t he orders : Tet ra2

375

in region Ⅳinstead of in region Ⅲ, as in t he sperma2 tozoon of Di pyli di u m cani n u m ( Miquel et al . , 1997) , A noplocephaloi des dent ate ( Miquel et al . , 1998) and R aillieti na ( R aillieti na ) t u netensis ( Bg et al . , 1994) .

p hyllidea , Phyllobot hriidae , Caryop hyllidea and some

Spermiogenesis and sperm ult rast ruct ure have

Tet rabot hriidea cestodes wit hout an intercent riolar

been used successf ully as a p hylogenetic character in

body ; Type Ⅲ, wit h only one flagellum ; spermio2

cestodes. Moreover , cytochemical and immunocyto2

genesis involves no flagellar rotation but proximo2dis2

chemical met hods , which could be employed to t race

tal f usion does take place ; claimed to occur in some

metabolic event s during spermatogenesis , could prove

Cyclop hyllidea cestodes ( genera : Nem atot aenia , M at hevot aenia , R aillieti na ) ; Type Ⅳ, wit h only

f ruitf ul in developing new approaches in t he cont rol of

one flagellum ; during spermiogenesis neit her flagellar

parasites.

rotation nor proximo2distal f usion was observed in some cestodes of t he order : Cyclop hyllidea ( Anoplo2

Acknowledgements  All of t he work recorded here

cep halidae , Thysaniezia , Hymenolepis , Aporina) .

was undertaken at t he School of Biology and Bio2

reproduction of t his economically important group of

Spermiogenesis in M oniez ia ex pansa is similar

chemist ry , Medical Biology Cent re , Queen’s U niver2

to type Ⅳ, but differs in showing spiral rootlet s at t he bottom of t he two cent rioles ( very different to t he

sity Belfast , U K. Appreciation is extended to George

st riated rootlet s found in t rematodes and in some ot h2

st udent s : L ucinda Campbell , Susan Robert s , Michael

er cestodes ) and might connect to t he nucleus.

Stewart , Liam Halferty and Myles Meaney for t heir

Whet her t hey resemble t he rootlet filament s of cent ri2 oles in protozoans which connect to t he nucleus ( and

kind help .

are t herefore cont rolled by nuclei) is unclear and war2 rant s f urt her st udy. 313  Spermatozoon of Moniezi a expa nsa Concerning t he morp hology of t he spermatozoon in M oniez ia ex pansa. Swiderski ( 1968 ) stated t hat t he spermatozoon is a very elongate , spindle2shaped

McCart ney for technical assistance and to graduate

References Bg , C. T. and B. Marchand ,  1992  ∗ tude ultrastructurale sur le spermatozogde de Moniezia ex pansa et M . benedeni ( Cestoda , Cyclophyllidea , Anoplocephalidae ) .

A nn .

Parasitol .

Hu m .

Com p . ( Paris) 67 : 111 - 115.

Bg , C. T. and B. Marchand  1994  Ultrastructure of t he spermiogen2 esis and t he spermatozoon of Raillieti na ( Raillieti na) t unetensis

cell , twisted in a loose spiral. In our st udy , t he sper2

(Cyclophyllidea , Davaineidae) , intestinal parasite of turtle doves in

matozoon is filiform , it s twisted , loose spiral appear2

Senegal. I nt . J . Parasitol . 24 : 237 - 248.

ance may be caused by t he movement of t he sperma2 tozoon. In our work , at least 37 sections show t he spermatozoon in st raight orientation. Bg et al . ( 1992 ) had shown for t he first time t hat t he exis2 tence of an axoneme which does not reach t he ex2 t remities of t he spermatozoon in M oniez ia ex pansa and M .

benedeni . They divided t he spermatozoon

Han , Y. R.  2001  Molecular Cell Biology , Second Edition. Beijing : Science Press , 505 - 506. J ustine , J . L .  1998  Spermatozoa as phylogenetic characters for t he Eucestoda. J . Parasitol . 84 (2) : 385 - 408. Miquel , J . and B. Marchand  1997  Ultrastructure of t he spermato2 zoon of Di pyli di u m cani nu m ( Cestoda , Cyclophyllidea , Dilepidi2 dae) , intestinal parasite of Canis f amiliaris. Parasitol . Res . 83 : 349 - 355. Miquel , J . and B. Marchand  1998  Ultrastructure of t he spermio2

into five distinct regions and described t he nucleus as

genesis and t he spermatozoon of A noplocephaloi des dentata ( Ces2

appearing in region Ⅲ. We also found t hat t he ax2

toda , Cyclophyllidea , Anoplocephalidae) , an intestinal parasite of

oneme does not extend to t he very anterior end. Moreover , before it reaches t he posterior ext remity , it grows out of t he body of t he spermatozoon in region

Ⅴ and becomes a f ree flagellum. The nucleus appears

Arvicolidae rodents. J . Parasitol . 84 : 1 128 - 1 136. Mahendrasingam , S. , I. Fairweat her and D. W. Halton  1989   Spermatogenesis and t he fine structure of t he mature spermatozoon in t he free proglottis of T rilocularia acant hiaev ulgaris ( Cestoda , Tetraphyllidea) . Parasitol . Res . 75 : 287 - 298.

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Swiderski , Z.  1968  The fine structure of t he spermatozoon of sheep tapeworm , Moniezia ex pansa ( Rud. , 1810 ) Cyclophyllidea , Anoplocephalidea. Zool . Pol . 18 : 475 - 486. Rosario , B.  1964  An electron microscope study of spermatogenesis in cestodes. J . Ult rast ruct . Res . 11 : 412 - 427. Rybicka , K.  1966.  Embryogenesis in cestodes. A dv . i n Para2 sitol . 4 : 107 - 186.

Tian , X. , L . Yuan , Y. Li , X. Huo , X. Han , M. Xu , M. L u , J . Dai and L . Dong  1998a  Ultrastructural observation on sperma2

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tocytogenesis in taeniid cestodes. Chi . J . Parasitol . Para. Dise. 16 : 209 - 212. Tian , X. , L . Yuan , Y. Li , X. Huo , X. Han , M. Xu , M. L u , J . Dai and L . Dong  1998b  Ultrastructural observation on t he transformation of t he spermatozoon in spermatogenesis of taeniid cestodes. Chi . J . Parasitol . Para. Dise. 16 : 269 - 273. Xylander , W. E. R.  1989  Ultrastructural studies on t he reproduc2 tive system of Gyrocotylidea and Amphilinidea ( Cestoda) : sper2 matogenesis , spermatozoa , testes and vas deferens of Gy rocotyle. I nternational J . Parasitol . , 19 : 897 - 905.

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Li Hai2 Yun et al . : Spermatogenesis , spermiogenesis and spermatozoon in t he cestode

377

Explanations of plates Plate Ⅰ Transmission elect ron micrograp hs of spermatogenesis in t he cestode ( M oniez ia ex pansa ) 1. Section of testicular follicle , showing cells in different stages of development  ×3 032  Scale = 2 μm 2. A part of a follicle showing primary ( Psg) and secondary spermatogonia ( Ssg)  × 6 885  Scale = 1 μm 3. Primary spermatocytes ( Psc) showing synaptonemal complex in t he nuclei and centrioles (C) arranged at right angles in t he cytoplasm near t he nu2 cleus of a cell  ×6237  Scale = 1 μm 4. High magnification of a synaptonemal complex  ×22 000  Scale = 015 μm 5. Secondary spermatocytes ( Ssc) , which are characterized by t he arrangement of mitochondria ( m) , connect to t he common cytophore  ×3 611   Scale = 2 μm 6. A cytophore (Cp) . Note t he spematid connected to t he cytophore by a narrow cytoplasmic stalk at bottom right  ×5 029  Scale = 2 μm

Plate Ⅱ Transmission elect ron micrograp hs of spermiogenesis and spermatozoa in t he cestode ( M oniez ia ex pansa ) 7. Longitudinal section of a differentiation zone , showing spiral rootlets (arrow) connecting to centrioles and t he presence of spiral cortical microtubules (Cm)  ×15 810 Scale = 015 μm 8. Spermiogenesis. Longitudinal section of a differentiation zone , showing an axoneme (Ax) growing out of a centriole (C) directly into t he cytoplas2 mic extension. The nucleus (N) shows a typical conical shape  ×17 655  Scale = 015 μm 9. Appearance of crest2like body (Cb) followed by a constriction of t he ring of arched membranes. Amorphous electron2dense material condenses at t he level of anterior extremity of t he spermatozoon forming t he apical cone (Ac) of t he spermatozoon  ×25 263  Scale = 015 μm 10. Mature spermatozoa detach from t he residual cytoplasm , which remains in t he testicular follicle as an electron2dense residual body ( Rb)  ×4 620

 Scale = 2 μm 11. Cross sections of regions Ⅰ: ①, Ⅱ: ② and Ⅳ: ④ ×20 628  Bar = 015 μm 12. Cross sections of regions Ⅲ: ③ and Ⅳ: ④ ×17 778  Bar = 015 μm 13. Cross sections of regions Ⅱ to Ⅴ ( ②- ⑤)  ×22 620  Bar = 015 μm 14. Cross sections of regions Ⅳ: ④and Ⅴ: ⑤. Longitudinal sections of regions Ⅳ: ④and Ⅴ: ⑤. Some free flagella ( F) are among  ×13 415

 Bar = 015 μm 15. Longitudinal sections of regions Ⅱ: ② and Ⅲ: ③ ×11 765  Bar = 1 μm 16. Longitudinal sections of regions Ⅱ: ②, Ⅳ: ④ and Ⅴ: ⑤ ×19 670. Bar = 015 μm Am : Arched membrane  Cp : Cytophore  m : Mitochondrion  N : Nucleus  Psc : Primary spermatocyte  R : Residual cytoplasm  Rb : Residual body  Ssc : Secondary spermatocyte  Spd : Spermatid  S : Spermatozoon

L I Hai2 Yun et al . : Spermatogenesis , spermiogenesis and spermatozoon in t he cestode ( M oniez ia ex pansa ) ( Cyclop hyllidea , Anoplocep halidae)

  Explanation at t he end of t he text

Plate Ⅰ

L I Hai2 Yun et al . : Spermatogenesis , spermiogenesis and spermatozoon in t he cestode ( M oniez ia ex pansa ) ( Cyclop hyllidea , Anoplocep halidae)

  Explanation at t he end of t he text

Plate Ⅱ

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动物学报  49 ( 3) :370~379 , 2003 A ct a Zoologica S i nica         Spermatogenesis , spermiogenesis and spermatozoon in the cestode ( Moniezia expa nsa ...

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