222 C. O. WHITMAN. 



are in general round, homogeneous, without the sliglitest trace 

 of nuckar formations. The transparency of these spheres varies 

 directly as their size. The minute granules are quite opaque. 

 From all this I conclude that the spheres arise from the granules 

 by a simple process of growth. This agrees in a striking manner 

 with the results reached by Gcgenbaur in his investigations of 

 the vertebrate egg (-/J^). The chief difference is, that in the 

 vertebrates (birds, reptiles) the yolk develops farther than in 

 Clepsine, differentiating into white and yellow yolk. 



Summary. — 1. The egg-string consists of a central, nucleated 

 protoplasm (rhachis), and a peripheral cellular layer. 



2. The primary egg-cell, the development of which into the 

 mature egg requires about two weeks, arises (probably) from the 

 rhachis. 



3. The precipitation of yolk-granules takes j)lace with the 

 greatest energy in the axis of the rhachis, but is at no time 

 localised here. 



4. The yolk-spheres arise by a simple growth of the yolk- 

 granules. 



II. Copulation, Deposit of Eggs, &c. 



Copulation. — As is well known, Clepsine, like all the Hirudinea, 

 is hermaphrodite. Copulation has never been observed. Whether 

 the worm can fructify itself, or whether a union of twoindividuals 

 is necessary to this end; whether in the latter case the frnctili- 

 cation is reciprocal; whether the impregnation takes place within 

 or without the body ; all these are ciucstions with respect to 

 which there has been the greatest diversity of opinion. 



I have kept large numbers of Clepsine in small glass-aquaria 

 during two summers and a few over winter. When ])r()})('rly 

 cared for, they thrive and jjroduce eggs in abundance. 1 have 

 generally examined the glasses four or five times a day, besides 

 keeping a few in a glass brfore me while at work. I have often 

 seen several individuals lying side by side, or across one another 

 for hours at a time ; but I have never seen them in a position 

 that would admit of sexual union. 



Filippi (;] j) and some other naturalists mentioned by Moquin 

 Tandon (tw)> regarded it as highly probable that Clej)sine was 

 capable of self- fructification, this act being performed at the 

 time the eggs were laid ("emettendo ad un tenq)o le nova cd il 

 liquor seminale.") 



(irube (5*J) inferred from the fact that he never found sper- 

 matozoa on fresh laid eggs that inq)regiiation took ])lace within 

 the body, llathke makes no mention of the matter. Leuckart 

 ((T7t) thinks it probable that copulation and recij)rocal fecunda- 

 tion take place. According to Kobin (',V') the eggs first come 



