218 C. O. AVUITMAN. 



work ('I'). In the case of Clepsine, Robin (Vt) fidmits that 

 no proj)er ovo-spermatophores exist, and claims only to have 

 found something analogous. As the ovo-s])ermatophore-tlieory 

 was corrected by Leuckart, refuted by O. Hertwig (i|) in the 

 case of Nephelis, and practically abandoned by Robin himself in 

 Clepsine, it will be unnecessary to devote further attention to ir. 

 There are then two views with reference to the formation of 

 the egg : — 



1. (Leydig). — It arises from ^ free nucleus, which^ with other 

 nuclei, lies imbedded in a common protoplasmic mass. 



2. (Leuckart). — It arises from a readt/ formed cell. As 

 neither of these investigators made use of sections in the study 

 of the egg-string, it is evident that their statenieuts have refer- 

 ence to tlie peripheral j)art alone. 



Reprodactive Organs. — The exiernal orifices of both kinds of 

 sexual organs are found in the median ventral line of the seventh 

 body-segment, the male in the tirst and the female in the last 

 (3rcl) annulus of this segment. The ovaries are two elongated, 

 tubular sacs, lying on each side of the nerve-chain, between this 

 and the testicular sacs, and extending backwards from the vagi- 

 nal aperture through two or three body-seginents. They show 

 no differentiation into ovarium, oviduct, and uterus, but are of 

 nearly uniform size, form and structure, from the vaginal to the 

 csecal ends. Just behind their common orifice they stand in 

 open communication with each other, so that the contents of 

 the one may be, and often are, partially at least, driven into the 

 ither. 



The Egg-string. — In each sac there is a single, much-twisted 

 egg-string. No connection between this string and the wall of 

 the sac exists in the mature worm, although such a connection 

 may have existed at an early st;ige in the development of the 

 ovaries. I have succeeded in isolating this string tsevcral tiims 

 without, breaking it, and found that the thin membrane covering 

 it is closed at both ends. The strings lie bathrd in a nourish- 

 ing (?) fluid, in which float some cells, which, as Leydig remarks, 

 have probably arisen from the epithelium of the sacs. One of 

 these strings, measured at a time when tlie largest eggs were only 

 about '1 mm. in diam., bad a diameter of '-i — "f mm. at the hind 

 end. From this ])oint it ta[)ered gradually to the fore end, where 

 the diameter was "1 mm. The larger eggs were; found near the 

 hind end and the smaller at the fore hind, while between these 

 points were all intermediate sizes. The string is composed of 

 two well-defined parts, a central and 7i peripheral. 



\. TheUhach'u.—'\\\^. central part (PL XI II, lig. 57), which I 

 will Imnceforth designate as r/iacJiis, attains its maximum di- 

 ameter by the time the eggs iner.sure between "3 and "4 nun. 



