EMBRYOLOGICAL INVESTIGATIONS 263 



experiments made by Driesch on Echinoid eggs, 

 which when artificially warmed were found to have 

 a marked tendency to develop twin-embryos. 



Another line of research was initiated independ- 

 ently by Chabry and by Roux, who investigated 

 the effects of injuring or destroying one of the two 

 or four blastomeres resulting from the first or 

 second cleavage of the egg. Chabry, whose results 

 were published in 1887, use< ^ f r h* 5 experiments 

 the egg of an Ascidian, Ascidia aspersa. Taking 

 eggs in which segmentation had just commenced, 

 and division into two cells had been effected, he 

 destroyed one of the two cells by pricking with a 

 needle. Under such circumstances he found that 

 the surviving cell developed into a half-embryo. 

 By experimenting in similar manner on eggs which 

 had divided into four cells or blastomeres, he was 

 able to produce either quarter, half, or three-quarter 

 embryos. Chabry concluded from his results that 

 each blastomere, at any rate in the early stages of 

 development, has a determined destiny and repre- 

 sents a definite part of the larva. This view was 

 first propounded by Professor His who, in 1874, 

 maintained the existence of " special regions in the 

 germ, which give rise to special organs," and held 

 that each organ of the embryo is represented by a 

 definite part of the body of the egg. 



This view is closely similar to the old doctrine of 

 " Evolution" or "Preformation," according to which 

 it was held that all the organs and parts of 

 the embryo were already present in the egg when 

 laid; and that development consisted in an unfolding 



