GERMINAL VESICLE AND FIRST EMBRYONIC NUCLEUS. 177 



contents of the germinal vesicle became dissolved in the 

 vitelline protoplasm. This identity of the phenomena which 

 lead to the disappearance of the germinal vesicle in the star- 

 fish on the one hand, and the hydra on the other, is so sig- 

 nificant that it is needless to insist upon its importance. 



The fact of the dissolution of the nucleolus in the nuclear 

 substance is not an isolated fact. I have long ago observed 

 the alternate disappearance and reappearance of nucleoli in 

 the nucleus of the Gregarinida. Strasburger states that the 

 fusion of the nucleoli in the body of the nucleus constantly 

 precedes the division of the nucleus ; and I have noticed the 

 same fact in my researches on the division of the cells in the 

 embryonic layers of the rabbit. I believe that what is true 

 of the nucleoli is true also of the nuclear membrane : the 

 substance which constitutes that membrane may be dissolved 

 in the nuclear substance. 



When, eighteen months ago, I made the observations of 

 which I have just given an account, I had the intention 

 also of studying the origin of the polar globules and the 

 mode of formation of the first embryonic nucleus. But I 

 was interrupted in my study of the earliest phenomena of 

 development by the opportunity which presented itself one 

 day when I had not any Asterida at my disposal, for inves- 

 tigating the origin of the sexual organs in Zoophytes, in 

 some organisms which came into my hands accidentally. 

 From the time when I entered upon the study of this question 

 in thelHydractinia, I thought I saw the possibility of arriving 

 at a positive solution of it. 1 abandoned for the moment the 

 study of the development of the Starfish ; reckoning on 

 being able to resume it when I wished ; but since that time 

 I have not again had the opportunity of completing my re- 

 searches. I have seen the directive bodies (Richtungsblaschen) 

 formed under my eyes, and I am in a position to affirm that a 

 fresh nucleus appears in the vitellus before the first segmen- 

 tation; but I am not in a position to say either how the 

 directive bodies appear, nor how the first nucleus is formed 

 in the embryo. 



If I compare the results of my study of the germinal 

 vesicle of the starfish with my observations on the rabbit, 

 I find a complete analogy as to the essential facts ; but also 

 differences the importance of which I do not wish to diminish. 

 In the rabbit as in the starfish the germinal vesicle dis- 

 appears in so far as it is a morphological element ; no part 

 formed by the germinal vesicle exists any longer in the ovum 

 at the moment when the first embryonic nucleus is seen to 

 appear ; no genetic bond then exist between the germinal 



VOL. XVI NEW SER. M 



