264 PROBLEMS OF FERTILIZATION 



cortical reactions cannot enter into the internal reac- 

 tions of fertilization. This might be due either to a 

 change in the spermatozoon itself during its passage 

 through the cortex, to a change in the internal proto- 

 plasm of the egg consequent on the cortical changes, 

 or to both combined. It would be difficult to separate 

 these possibilities, because we cannot isolate a spermato- 

 zoon that has been concerned in cortical activation 

 and introduce it into central protoplasm (endoplasm) 

 of another unactivated egg. 



However, a very ingenious experiment of Chambers 1 

 throws some light on the problem. It has been shown 

 by other experimenters (see p. 162) that portions of 

 fertilizable eggs are themselves fertilizable; such parts 

 possess a portion of the cortex (ectoplasm) of the egg. 

 Chambers has added a most interesting and significant 

 fact by showing that the internal protoplasm (endo- 

 plasm) of the starfish egg is not fertilizable. With the 

 microdissection needle he tore the cortex and allowed 

 endoplasm to flow out; this accumulates in spheres, 

 which may be of considerable size and may contain 

 the egg nucleus. Of forty to fifty such endoplasmic 

 spheres not one could be fertilized; on the other hand 

 the cortical material left behind, which rounds up into 

 a sphere in each case, is fertilizable. If an endoplasmic 

 mass which has flowed out of a tear be allowed to 

 remain connected with cortical material the mass is 

 fertilizable, and the regularity with which segmentation 

 of such a mass proceeds is a function of the amount 



T The writer is greatly indebted to Dr. Chambers for permission to 

 record these observations in advance of his own publication on the 

 subject. 



