Ch. Ill] EXPERIMENTS IN CROSS-FERTILIZATION 31 



fragment is penetrated by one spermatozoon, the fragment 

 develops. Such a fragment contains only half the number of 

 chromosomes of the normal fertilized egg.'^ Boveri isolated 

 some of these fragments, and said that they give rise to small 

 embryos normal in structure. Boveri stated, further, that if a 

 non-nucleated fragment of the egg of one species of sea-urchin 

 is entered by one spermatozoon of another species, the result- 

 ing larva is like the larva of the father (i.e. it is like the larva 

 of the individual from which the spermatozoon comes). If 

 this result should prove true,^ it would show that the nucleus 

 and not the protoplasm determines the character of the larva. 



1 Morgan, '95, Anat. Anzeigcr. 



2 Seeliger ('95) and myself ('95) have repeated Boveri's experiment and have 

 tried to sliow that the evidence on which Boveri based his conclusion in regard 

 to the paternal character of the crossed larva is insufficient. 



