446 BULLETIN OF THE 



nated while the eggs are still in the ovary, and are formed as in the star- 

 fish, with the exceptions as to number and as to their failure to raise 

 any sort of a pellicle. On account of the absence of a pellicle they are 

 soon lost after the exclusion of the egg. 



The errors of Van Beneden and 0. Hertwig relative to the fate of the 

 germinative vesicle are due, in his opinion, to the use of slight pressure 

 resulting in abnormal phenomena. Other cases (Sagitta and Phallusia) 

 are cited to show that the vesicle may early disappear. 



In Phallusia the " testa cells " arise within very young eggs and in 

 contact with the nucleus, but this is in no way to be compared with 

 the formation of polar globules, so that the sea-urchin is the only animal 

 whose eggs part with their polar globules while still within the ovary. 



In Heteropoda after the disappearance of the Wagnerian dot there ap- 

 pear two centres of attraction at the two extremities of the vesicle. The 

 rays of the stars, which announce the existence of these centres, extend 

 partly without and partly within the vesicle. The latter encounter and 

 unite with each other, beginning with those in the middle [axis of spin- 

 dle 1], to form the bipolar filaments of the first amphiaster. After the 

 second polar globule is formed, the varicosities of Biitschli pertaining to 

 the last aster reunite with the central mass of the aster to constitute the 

 female pronucleus. The male only makes its appearance when the sec- 

 ond polar globule is forming, notwithstanding fecundation is effected in 

 the oviduct long before. It is at first very small, extremely refringent, 

 and located at the surface of the yolk in a position variable as regards its 

 relation to the polar globules. In the starfish the male aster also re- 

 mains latent up to the same moment. At a certain stage in the growth 

 of both pronuclei there appears a minute nucleolus. The nucleus of 

 the fecundated egg has only a very remote connection with the germi- 

 native vesicle. 



The figures given by Brandt ('77^) to illustrate the formation of the 

 polar globules in Lymnaeus cannot be considered as giving a very com- 

 plete idea of the process. In the author's opinion (p. 591) the globules 

 are formed by a part of the amoeboid germinative vesicle swelling forth 

 in the form of a clear rounded drop in which an irregularly outlined nu- 

 cleus at once appears. It is only a portion of the germinative vesicle 

 which is thus expelled, the most of it returning as an amoeboid body into 

 the vitellus, where it becomes indistinct, but still persists, to give origin 

 to the nuclei of the first spheres of segmentation. Brandt's views of the 

 amoeboid nature of nuclei are elsewhere discussed. 



0. Hertwig ('77") gives in a preliminary paper the results of studies 



