MUSEUM OF COMPARATIVE ZOOLOGY. 447 



on the eggs of a number of animals made in the early part of the win- 

 ter of 1876-77, — therefore very nearly contemporaneous with Fol's 

 valuable investigations. As the ultimate illustrated papers (Hertwig, 

 '78 and '78"), giving more fully the results on w^hich this preliminary 

 communication is based, have already appeared, I will limit myself 

 here to a statement of Hertwig's general conclusions, and refer the 

 reader for details to the review of those papers which will be found 

 farther on. 



Hertwig has also discovered, independently of Fol, the existence of 

 polar globules* in Sphaerechinus brevispinosus, which were formed in 

 this case from eggs artificially removed with the ovarium and laid for 

 some time in sea-water. From all his observations Hertwig finds 

 confirmation of his previously expressed views on maturation and fecun- 

 dation, especially in three points: (1.) that the continuity in the 

 generations of nuclei is not interrupted ; (2.) that the polar globules 

 arise by a process of cell budding; and (3.) that fecundation depends 

 on the copulation of tivo nuclei. On the other hand, his opinion in 

 regard to the prevalence of polar globules is altered. He now believes 

 that a general agreement in this matter throughout the animal king- 

 dom will be established. The most important objective communication 

 in this paper is unquestionably the description given of the method in 

 which the first maturation spindle arises in Asteracanthion (see p. 452). 

 According to P. Mayer ('77, p. 199) the germinative vesicle disap- 

 pears, in the case of Pagurus, while the egg is still in the ovary, so that 

 when freshly deposited it is "positively enuclear." Of this he has 

 convinced himself by crushing the eggs, and has also often observed the 

 1 origin of a new nucleus. Before it perishes the vesicle is sometimes 

 I to be seen near the surface of the egg, — instead of the centre, where 

 I it always is at first, — surrounded with its protoplasmic area. This 

 ' eccentric position he regards as probably abnormal, and indicative of 

 an approaching disintegration of the egg. With the disappearance of 

 ! the vesicle the protoplasmic area surrounding it ceases to exist. For 

 I this reason a direct dispersion of the elements of the vesicle in the pro- 

 toplasm is the simplest assumption. The protoplasm, retaining its net- 

 like distribution, may subsequently secrete a new nucleus in its centre. 

 Since the existence of a distinct egg membrane (not affected by caustic 

 potash) and of the germinative vesicle appear to exclude each other ; 

 and since fecundation must precede the formation of the membrane, he 



* The existence of polar globules in the vsea-urchins was established by Agassiz 

 in 1867. See A. Agassiz, '64, p. 6, PI. I., '77, p. 7, PI. I., and •67«, p. 2. 



