Organisms from Eggs 151 



results disagree with the statement of Boveri and support 

 the observation of the writer. 



If we raise the question why such a Hmit exists in 

 regard to the divisibihty of Hving matter, it seems 

 probable that only those fragments of an egg are 

 capable of development into a pluteus which contain a 

 sufficient amount of material of each of the three layers. 

 If this be correct, it would certainly not suffice to mix 

 the chemical constituents of the egg in order to produce 

 a normal embryo ; this would require besides the proper 

 chemical substances a definite arrangement or structure 

 of this material. The limits of divisibility of a cell 

 seem therefore to depend upon its physical structure 

 and must for this reason vary for different organisms 

 and cells. The smallest piece of a sea-urchin egg that 

 can reach the pluteus stage is still visible with the naked 

 eye, and is therefore considerably larger than bacteria 

 or many algae, which also may be capable of further 

 division. 



8. The most important fact which we gather from 

 these data is that the cytoplasm of the unfertilized egg 

 may be considered as the embryo in the rough and that 

 the nucleus has apparently nothing to do with this 

 predetermination. This must raise the question sug- 

 gested already in the third chapter whether it might 

 not be possible that the cytoplasm of the eggs is the 

 carrier of the genus or even species heredity, while the 

 Mendelian heredity which is determined by the nucleus 



