258 



COMPARATIVE ANATOMY 



CHAP. 



penis. The bursa is a spacious sac-like invagination of the posterior 

 end of the body which can be evaginated in copulation. Three pairs. 



of cement glands are generally con- 

 nected ^yith the male apparatus, their 

 ducts entering the terminal division of 

 the vas deferens (ductus ejaculatorius). 

 Annulata. — The Hirudinea are 

 hermaphrodite. Their male genital 

 apparatus (Fig. 173) has the following 

 general structure. Several testes lie 

 in pairs segmentally arranged in the 

 middle region of the body, generally 

 between the' consecutive lateral diver- 

 ticula of the mid-gut, within the muscu- 

 lar septa separat- 

 ing these diverti- 

 cula ; the testes 

 thus divide these 

 septa into anterior 

 and posterior lam- 

 ell*. A short effer- 

 ent duct arises 

 from each testis. 

 The ducts of all 

 the consecutive 

 testes of one side 

 emerge into a vas 

 deferens which 



jno 



Fig. 172. — Representation, partly dia- 

 grammatic, of tlie organisation of a male 

 Ecliinorliynchiis. r. Proboscis with barbed 

 hooks, protruded ; r?ft, retractor muscles of 

 the proboscis : rs, proboscis sheath ; rn, 

 proboscis nerves ; g, cerebral ganglion ; re, 

 retinacula ; li, ligament ; s^^, longitudinal 

 nerves ; 7i, testes ; vd, vas deferens ; s&, 

 vesicnlEe seminales'; kd, cement glands ; gg, 

 common vas deferens ; gag^ genital gan- 

 glion ; &s, bursa ; mo, male genital aperture ; 

 i/i, body cavity ; ip, penis ; I, lemnisci. 



runs through the 

 whole length of 

 the testicle region. 

 In front of the 

 most anterior tes- 

 tis the two vasa 

 deferentia con- 



FiG. 173.— Genital or- 

 gans of Hinido. y, Penis ; 

 mo, male ; v:o, female geni- 

 tal aperture ; ov, ovaries ; 

 h, testicles ; vd, vas de- 

 ferens. 



verge towards the 



middle line, here to open outwardly by a common aperture, or in some 

 cases by a common unpaired copulatory apparatus (penis). 



The number of testes may in some cases be greatly increased {Nephelis, 

 LumbricobdcUa), and this probably results from the subdivision of each testis into 

 several vesicles. Complications often occur in the last portion of the vasa deferentia. 

 For example, in Hirudo, the vas deferens, before entering the penis through a short 

 terminal passage, forms a tangled coil on each side. Glands are often connected with 

 the penis. The male genital aperture in Hirudo is in the 10th segment, between the 

 30th and 31st rings. 



The female genital apparatus (Fig. 173) lies behind the male 

 aperture, and generally between the vasa deferentia. It consists of 



