446 ROHHRT T. HAXCE. 



attributes or determiners with which originally they must have 

 been equipped. If the latter interpretation is correct the per- 

 petuation of the complete mitotic mechanism in the soma as it 

 exists in the reproductive organs may seem, as far as any need for 

 an exact division of the genes is concerned, somewhat un- 

 necessary, to be classed possibly with vestigial organs and having 

 no more significance. In view of the great delicacy of the 

 mechanism that exists in all cells for accurately dividing the 

 chromatin the last suggestion does not seem impressive. But as 

 far as our morphological data on the behavior of somatic chiomo- 

 somes go, together with the behavior of the soma in growth and 

 regeneration, the above suggestion is at least a possibility to be 

 considered in our attempt to get at the physiology of development 

 and genetics. 



SUMMARY. 



1 . The chromosome number in the somatic cells of the chick is 

 about 35 or 36. 



2. No characteristic differences between the number, the sizes, 

 the morphology or the behavior of the chromosomes in com- 

 parison either with each other or with the cells of the gonads 

 have been noted. 



3. In view of the entire similarity of the somatic and germinal 

 mitotic behavior and in consideration of the complete inability 

 of highly specialized cells to regenerate other than cells similar 

 to themselves it is tentatively suggested as a basis for future 

 discussion that the somatic chromosomes, as far at least as their 

 genetic function is concerned, have either become functionless or 

 their cytoplasmic environment is incapable of reacting to the 

 possibilities presumably carried by them. 



BIBLIOGRAPHY. 



1. Hance, Robert T. 



"17 The Diploid Chromosome Complexes of the Pig (Sus scrofa) and their 

 Variations. J. Morph., Vol. 30, p. 156-222. 



2. Hance, Robert T. 



"18 Variations in the Somatic Chromosomes of (Enothera scintillans DeYries. 

 Genetics, Vol. 3, p. 225-275. 



3. Hance, Robert T. 



"25 The Fixation of Avian Chromosomes. Anat. Rec., Vol. 31, p. 87-92. 



4. Hance, Robert T. 



