Behavior of the Germ-cells 177 



the cytoplasm have not had time to act or to increase suffi- 

 ciently in amount to affect the development. Most embryolo- 

 gists seem inclined to ascribe the effects entirely to the nucleus, 

 which they believe dominates all the changes in the protoplasm. 

 On the contrary, I am inclined to think that it has not been 

 shown conclusively that this influence is nuclear in origin, but 

 may possibly be due to the protoplasm introduced with the 

 sperm. The slow increase in amount of the introduced proto- 

 plasm might account for the insignificant part it plays during 

 the early development, when it is very small in amount com- 

 pared to that of the egg-protoplasm. If, as others suppose, 

 the chromatin of the nucleus is the all-controlling influence, it 

 is difficult to see why this is not apparent at once, since the 

 nucleus of the hybrid has equal amounts of paternal and ma- 

 ternal material. It may be fairly claimed, however, that the 

 introduced sperm-nucleus requires time to change the protoplasm 

 into its own sort of material. 



The most striking case of the lack of influence of the sperm, 

 nucleus on the egg is that recently given by Godlewski. By 

 following Loeb's method and making the sea-water alkaline, he , 

 has succeeded in fertilizing the egg of the sea urchin (Echinus 

 and others) with the sperm of the crinoid (Antedon). The hy- 

 brids were of the sea-urchin type in all respects observed, includ- 

 ing the pluteus stage. 



Boveri carried out the ingenious experiment of fertilizing a 

 non-nucleated piece of the egg of one species of sea urchin with a 

 spermatozoon of another species. 1 The pluteus obtained was 

 purely paternal. He concluded that the result was due to the 

 introduced nucleus. Both Seeliger and I have taken exception 

 to Boveri's evidence on the ground that the hybrid pluteus that 

 can be obtained from nucleated pieces or from entire eggs is too 

 variable in its characters to give support to Boveri's conclusion. 

 In fact, some of these hybrids are so similar to the paternal 

 type that they cannot be distinguished from it. Godlewski's 



1 O. and R. Hertwig had previously shown that pieces of the sea urchin's egg 

 without a nucleus may be entered by spermatozoa of the same species. 



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