EXPERIMENTAL STUDY OF THE SEA URCHIN EGG 



29 



Experimental study of the 

 sea urchin egg 



Another method which we may use brings out additional information. 

 This involves the use of microdissection, a technique by which the egg is 

 actually cut up into parts and the development of the separated parts 

 followed. With the aid of a very fine glass needle we can press down on and 

 cut through the equator of the egg and thus separate the egg into two 

 halves, which round up to form two spheres, an animal half and a vegetal 



Fig. 11. The development 

 of animal and vegetal halves 

 of the sea urchin egg. The 

 egg is cut in two through 

 the equator by means of a 

 glass needle. The animal half 

 (right) is fertilized and de- 

 velops into a blastula (dauer- 

 blastula) but fails to form 

 endoderm. The vegetal half 

 (left) after fertilization forms 

 an incomplete embryo. 



ENDODERM 



DAUERBLASTULA 



