164 ANNELIDA [CH. 



Leeches are, like the earthworm, hermaphrodite, but their 

 Reproduc- reproductive organs differ in some respects from 

 tion - those of that animal. 



In Lumbricus the testes are repeated in two segments only, 

 but in Hirudo there are usually nine pairs of testes. The cavities 

 of both the testis and of the ovary are to be regarded as part of 

 the original coelom; in strictness the testes probably correspond to 

 the vesiculae seminales in an earthworm, which are part of the 

 coelom, and enclose the true testis and the sperm-funnel. Each 

 testicular sac produces spermatozoa on one side and on the other 

 side is ciliated. The ciliated tract is the sperm-funnel and leads 

 into a short transverse duct which passes into a longitudinal canal 

 termed the vas deferens, there being one such canal on each side 

 of the body. At its anterior end each vas deferens passes into a 

 convoluted mass of tubes the so-called epididymis whose walls 

 secrete a substance which binds the spermatozoa together into 

 packets called spermatophores. From each epididymis a short 

 duct passes towards the middle line, and these two ducts fuse and 

 enter the base of the penis, which is protruded from the segment 

 which contains the sixth distinct post-oral ganglion. The base of 

 the penis is surrounded by glandular cells which discharge into it 

 and which collectively are termed the prostate gland. They form 

 a milky fluid in which the spermatophores are bathed. It is to be 

 remembered that the names epididymis, prostate, etc., are given from 

 fanciful resemblances to parts in the anatomy of man by no means 

 homologous with the organs bearing the same name in the leech. 



The penis is simply the muscular end of the conjoined male 

 ducts or vasa deferentia; it is the organ by which the spermatophore 

 is deposited in the body of another leech. The spermatozoa in 

 Clepsine seem to penetrate the skin at any point and make their way 

 to the ovaries, where they fertilise the eggs. In other species the 

 spermatozoa enter in the usual way by the female genital pore. 



As in the earthworm, there is but one pair of ovaries. These 

 are minute filamentous bodies each enclosed in a small coelomic sac. 

 From each sac a short oviduct proceeds and uniting with its fellow 

 forms a twisted tube surrounded by many glands. This finally opens 

 by a median pore on the segment behind the one bearing the male 

 opening. 



Thus in leeches, unlike the condition in the earthworm, the 

 genital pores are single and median. The medicinal leech lays 

 its eggs in a cocoon and buries them in holes in the banks of the 



