THE MAMMALIAN EGG 



quarter of the nineteenth century was the Golden Age for gametol- 

 ogy, marked by the enthusiasm with which an increasing number 

 of investigators contributed information on an ever- widening range 

 of animal types, both vertebrate and invertebrate. As early as 1891, 



Fig. 6 



A few diagrams from the extensive series published by Sobotta 

 (1895) on fertilization in the mouse egg. 



Boveri was able to present a review of knowledge on fertilization 

 which, through its detail and insight, maintains an authoritative 

 status to this day. The trend of research in the present century on 

 the structure and function of gametes has been rather to support 

 and extend theories founded in the last century than to establish 

 new ideas — a feature that, as Oppenheimer (1957) points out, is 

 common to the science of embryology as a whole. 



Formal morphological studies on mammalian eggs were soon 

 accompanied by experimental work on isolated specimens. Schenk 

 (1878) seems to have been the first to contribute in this field, by 

 maintaining eggs in vitro and attempting to procure their fertilization 

 under these conditions. Though his methods were remarkably 

 advanced for his day, they were not apparently successful. Heape 

 (1890) holds precedence for the transfer of living eggs from one 

 animal to another and thus obtaining the birth of young from 

 unrelated foster-parents. Long (1912) prepared some of the earliest 

 cinematographic records of the changes shown by living eggs in 



