222 DESCRIPTIONS OF PREPARATIONS. 



Externally to each vas deferens and alternating in position with each 

 testis, is a row of globular sacs only a very little less in size than the testes 

 themselves. These are the vesicles of the segmental organs or nephridia. 

 Each vesicle opens by a pore on the last annulus of its somite. In front of 

 it, and in part externally to it, is a loop-shaped body. This is the chief part 

 of the nephridium, representing the main and apical lobes of that organ. 

 A narrow caecal process passes inwards from it and lies upon a testis. 

 This is the testis-lobe which ends in the nephridial funnel or nephrostome. 

 The funnel lies in a vascular sinus, the perinephrostomial sinus, or the 

 moniliform heart of Brandt. The two pair of nephridia lying behind the 

 last pair of testes in the twenty-first and twenty-second somites (Whitman), 

 possess these sinuses as well as funnels, but this is not the case with the 

 five first pair of nephridia which correspond to the somites six to ten 

 (Whitman). There are in all seventeen pairs of these organs. 



The azygos and median position of the generative pores is a noteworthy 

 feature, as is also the development of a muscular intromittent organ. It is 

 doubtful however whether they are of any importance in determining the 

 affinities of Hirudinea. 



The ductus ejaculatorius, according to Leuckart, has a stratum of circular 

 muscle fibres in its walls. The vas deferens ' is surrounded by a space or sinus 

 packed with cells, ' which possess a rather degenerate appearance ' (Bourne). The 

 sacs in which the true ovaries are lodged contain similar amoeboid corpuscles. It 

 has been suggested by Gibbs Bourne that these spaces represent a portion of the 

 original coelome, and the cells original blood corpuscles, and that they have been 

 closed in by the growth of the connective tissue before haemoglobin appeared in 

 the blood-plasma. 



The true ovary is a filamentous body, 10 mm. long in some instances. It is 

 coiled within the ovarian capsule. The oviduct opens into the capsule, but it is 

 not simply continuous with the walls of that space. On the contrary, its anterior 

 end is disposed in coils within it. These facts support the view quoted above from 

 Gibbs Bourne as to the nature of the capsule. The median or single portion of 

 the oviduct is surrounded by glands, by which the albumen mixed with the ova in 

 the cocoon is secreted in all probability. The vagina has muscular walls, is lined 

 by cuticle, and receives the spermatophores in congress. These bodies are stated 

 to contain not only spermatozoa, but corpuscles similar to those found in the coils 

 of the vesiculae seminales. They are resolved in the vagina, and the spermatozoa, 

 now free, are said to penetrate into the ovarian capsules. 



The ovarian capsules are sometimes of great length, as in Nephelis and Clep- 

 sine. In these genera * egg-strings,' produced by the continuous division of a cell, 

 lie free in the capsular cavity. The formation of the string from a ridge of the 

 epithelium lining the capsule has been observed in Nephelis. The ova sometimes 

 degenerate, and Schneider states that they are destroyed by amoeboid cells in the 

 ovarian capsule. The same thing occurs with the spermatozoa. But the full 



