Miscellaneous. 431 



Lastly, at the moment when the ovum arrives at maturity, the little 

 columns are ruptured, leaving no traces except slight thickenings of 

 the vitelline membrane at the points where they were attached. 

 We have then, therefore, a central granular mass in which the 

 germinal vesicle is no longer directly observable, and round this 

 mass a transparent zone which separates it from the vitelline mem- 

 brane. 



Prof. Harting has seen, in the ova of Ct/anea LamarcJcii and C. 

 capiUata, the stage in which the little columns exist * ; but not 

 having completely followed the preceding phases, he has given an 

 erroneous interpretation of the appearances observed. He regards 

 the ova of the Cyanece as furnished with a vitelline membrane of 

 considerable thickness and pierced with a great number of pores 

 leading from the outside to the interior, such, he says, as are met 

 with in the ovum of some Mammalia, perhaps in all, and also in the 

 ovum of many Teleostean fishes, in which, however, these pores 

 acquire much more considerable dimensions. It is evident that 

 these supposed pores are nothing more than the columns of clearer 

 protoplasm above mentioned. In this way the suppositions of 

 Harting with regard to the physiological function of these pores 

 also fall to the ground. He believed them to serve for the respira- 

 tion of the ovum, aud perhaps also for the passage of the spermato- 

 zoids. 



The preceding observations were made at Wimereux during the 

 month of September 1875. They are a part of a set of researches, 

 still unfinished, on the development of the Medusae ; and I have only 

 decided to publish them now because they appear to me to acquire 

 a much greater generality and importance than I at first supposed, 

 in consequence of the magnificent researches of Weismann f on the 

 ovum of the Daphnoideas. 



Weismann has observed a process precisely similar to that just 

 described, in the formation of what he calls the shell (Schale) of the 

 winter egg of the genera Pohjphemus^ Sida, and Daplmella. It is 

 remarkable that, in this case, as in that of the IVledusae, the ovum 

 undergoes a tolerably long incubation in a special medium furnished 

 by the maternal organism. 



The excretion of the hyaline vesicles, which takes place aU over 

 the periphery of the vitellus of the ovum of Bhizostoma, may in 

 other animals be confined to one point of the surface ; the pheno- 

 menon would then take on the appearance of the issue of excreted 

 globules. Considering this process, we may inquire whether the 

 phenomenon so often noticed of the rejection of a certain part of the 

 vitellus at the moment of the maturation of the ovum must be 

 regarded as equivalent in all animals in which it has been ob- 

 served. Biitschli has shown most clearly that the polar corpus- 

 cles of the ovum of Limnceus, Sucmica, Nephelis vulgaris, and Cuciil- 

 lanus eleyans originate by the process of cell-division. I may add 



* Niederlandisches Archiv, Bd. ii. Ileft iii. 



t Zcitsch. fiir wiss. Zool. Bd. xxviii. Heft 1 .& 2. 



