258 



INTERNAL FACTORS 



IV. i 



normal egg ; the chromosomes in the other cells are all 

 diminished, and no cell contains chromosomes of both kinds. 

 Further, the number of whole chromosomes may be 5 in one 

 cell and 3 in the other, or 4 and 3, or 3 and 3, or 4 and 2, or 

 3 and 2. 



Boveri concludes, it seems with perfect justice, that it is the 

 (vegetative) cytoplasm which has determined that the chro- 

 mosomes it contains shall remain whole, while, contrariwise, the 

 animal cytoplasm of the other cells brings about the process of 

 diminution. 



In Ascaris lumbricoides there is a diminution of the chromosomes 

 very similar to that seen in A. megalocephala, and, to judge from 



FIG. 156. Pluteus of Sphaerechinus granulans from in front and from 

 the side. (After Boveri, 189G.) 



certain abnormalities similar to those just mentioned, brought 

 about by the same means (Bonnevie). In Dytiscus there is some- 

 thing like a diminution of the chromatin in the nurse-cells, while 

 the oocyte retains all the chromatic material intact (Giardina). 

 The distinction seen here may, however, only be that observed in 

 all ova between the nutritive and reproductive functions of the 

 nucleus (trophochromatin and idiochromatin). 



5. Boveri's hybridization experiment, on which rests the 

 assertion that the nucleus alone conveys the inheritable characters 

 of the species, was as follows. 



The Plutei of Sphaerechinus granularis and of Echinus micro- 

 tuberculatus were found (at Naples) to be markedly different. 



