142 Dr. 0. Zacharias on the Reproduction and 



the surrounding tissue is considerably less than that which 

 exists between the latter and the chitinous lining of the 

 pharynx. It is therefore to the accidental existence of such 

 a difference that we must ascribe the particularly early recog- 

 nition of the pharynx in Rotifer. 



Then there is in the posterior part of the embryo a small 

 vacuole-like cavity, the early existence of which must be 

 recognized. At the spot where this cavity is to be observed 

 in embryos of Rotifer we see in young animals of Lucinu- 

 laria, Stephanoceros, Floscidaria, &c, small aggregations 

 of granules (so-called " urinary concretions ") which seem to 

 be enclosed in a special vesicle. I am uncertain whether 

 from the existence of these concretions the presence of a prim- 

 ordial kidney may be inferred, and only mention the inter- 

 esting fact that Aubert also has observed in the embryo of 

 Aspidogaster conchicola " two remarkable black points or 

 spherules," of which he says that they strongly refract the 

 light, have a stratified appearance, and constantly occur at the 

 same spot (between the ventral sucker and the intestine) *. 

 This is evidently perfectly analogous to the cases above 

 referred to in connexion with the Rotatoria. 



When the embryo of Rotifer vulgaris has advanced so far 

 that it presents an exact likeness of its parent on a smaller 

 scale, it begins to move briskly, and during this the uterine 

 vesicle (poche de maturation) in which it is enclosed is in 

 course of time ruptured. It is now quite free between the 

 intestine and the body-wall, which space constitutes a sort of 

 nursery for it after it has undergone the first act of its birth. 

 We see such embryos, i. e. young Rotifers, creep about 

 actively within the body of the parent, and frequently also 

 the jaw-plates of the young animals are in clapping move- 

 ment. In some cases I have seen such embryos with per- 

 fectly unfolded rotatory organs, making experimental vortices 

 within the body- cavity of the parent. But this has occurred 

 only two or three times during my investigations of many 

 months. 



I have already mentioned that I have never been able to 

 see how the mature embryo escapes from the body of the 

 mother, and is, so to speak, born for the second time. I 

 doubt that the porlal through which the young creature quits 

 the narrow domain of its development is to be found in the 

 cloacal aperture. The terminal intestine and the contractile 

 vesicle alone open into this aperture. It must remain for 

 other students of the Rotatoria to solve the mystery of the 



* Zeitschr. f. wiss. Zool. vi. (1855), p. 370. 



