Baer understood that the discovery of ovum division, 

 from which the development of amphibia begins, represented 

 a fundamental discovery in embryology. Against the importance 

 of this phenomenon, he admitted that an objection might be 

 raised "if in other animals there is nothing which is similar. 

 We, however, suspect that they have these phenomena" (p. 505) . 

 In fish, in Baer's opinion, it is impossible to see the 

 division clearly because of the transparency of their eggs, 

 and in birds he assumed that division into many small grains 

 takes place, but in another form. "I consider," he concluded, 

 "that the division of the yolk mass is a prototype of all 

 histological isolation" (108) . 



Returning in his later memoirs^ to the discovery of ovum 

 division in amphibia, Baer said that the study 



of the preparatory stage of development which is 

 the auto trans formation of material by continuous 

 division (led him) to the innermost sanctuary of 

 the history of development, as was subsequently 

 shown through the corroboration of countless 

 investigations .... A similar process of 

 division was observed in different animals as a 

 consequence of fertilization, in the form of 

 division of all yolk mass, or in the form of 

 division of small layers of the latter, which I 

 called the rudiment. 



Further in his autobiography, Baer discussed the behavior 

 of nuclei during division. At first the nucleus has a rounded 

 form, then is enlarged and stretched. Its center becomes 

 narrower and the nucleus takes a biscuit form; then the 

 substance of the nucleus disperses into different directions, 

 forming two small bodies. The division of the ovum itself 

 follows the division of the nucleus. Baer wrote that the 

 situation is like that of two rulers, originating by division, 

 each of whom collects around itself part of the kingdom in order 

 that after a short period of quiescence it may again separate, 



14. Baer, NACHRICHTEN, pp. 381-383 (377). 



426 



