1U HISTORY OF THE EGG FROM FERTILIZATION TO CLEAVAGE. 



processes will be described under the head of maturation, which, in 

 another egg, will be referred to fecundation or copulation. It might be 

 supposed that parthenogenetic eggs would furnish a means of distin- 

 guishing the two classes of phenomena, and the researches of Weismann 

 and Ischikawa certainly promised very much in this direction. But 

 Platner's discovery of two polar globules in the eggs of Liparis Sispar, 

 which were found to be able to develop without fertilization, seems to 

 upset Weismann's ••numerical law," and to point in another direction for 

 the settlement of the polar globule question. The whole subject is 

 involved in mystery, and the possibility is now before us of finding 

 that two polar globules are virtually produced even in those cases of par- 

 thenogenesis where only one has been discovered. Boveri has already 

 shown how the nuclear elements of two polar globules may be combined 

 in one, and actually removed from the egg by a single act of caryokinetic 

 division. Although it now appears highly improbable, it is nevertheless 

 possible that some eggs may be found in which the whole course of 

 maturation and impregnation is completed without the formation of free 

 polar globules, or even without the intercurrence of a single caryokinetic 

 division. Until the process of fecundation is better understood, it will 

 be impossible to find any criterion for distinguishing sharply between the 

 phenomena in question. The distinction proposed by Van Beneden be- 

 tween copulation and fecundation is of but little help so long as we remain 

 in uncertainty as to whether the active element in caryokinesis is cyto- 

 plasm or caryoplasra. The observations of Vejdovsky. Platner. Boveri, 

 and Boehm find the active agent in the cytoplasm, but who can say that 

 the aerdrosoma of Boveri, the primary aster of Platner and Boehm, is not 

 a nuclear derivative? If it is introduced into the egg with the sperma- 

 tozoon, as supposed by Boveri, we have no means at present of deter- 

 mining its precise origin. The relation of this body to the archoplasm, 

 pole-plasm, or periplast, has still to be determined. 



The difficulty in the way of separating these phenomena into distinct 

 classes is seen still in another way. The blastodisc of the fish-egg forms 

 in many cases entirely independently of fecundation. In pelagic eggs it 

 usually forms after the copulation of the sexual cells, and we have the 

 best grounds for believing that the process is profoundly influenced by the 

 presence of the spermatozoon. One may easily convince himself of this 

 by watching the process through, in both fertilized and unfertilized eggs. 



