THE CHROMOSOMES OF THE CHICK SOMA. 



ROBERT T. HANCE, 



THE ROCKEFELLER INSTITUTE FOR MEDICAL RESEARCH AND THE ZOOLOGICAL 

 LABORATORY, UNIVERSITY OF PENNSYLVANIA. 1 



The accumulated evidence in favor of the chromosomes being 

 in some way concerned with the determination and control of the 

 somatic characters has become so impressive as to be almost un- 

 assailable despite the possible objection of a few that the last 

 link in the chain (a demonstration of the actual activity of these 

 nuclear bodies as hereditary character bearers), due to the 

 deficiencies in our knowledge of cell chemistry, has yet to be 

 forged. This latter point is one about which geneticists and 

 cytologists are, at present, not greatly concerned and conclusive 

 data upon the physiological behavior of the chromosomes does not 

 seem at all imminent. While information is gradually accumu- 

 lating in preparation for this final analysis much may still be 

 accomplished by purely morphological studies with tentative 

 interpretations of physiological activity based on these observa- 

 tions. A recent study of the chromosomes associated with sex 

 in the chick (5) involved extensive observations on the chromo- 

 somes of dividing somatic cells, the results of which are recorded 



below. 



OBSERVATIONS. 



The technique of preparation (3), of counting and measuring 

 the chromosomes, the amount and source of the material (5) have 

 all been recorded and need not be repeated here. The chromo- 

 somes of over 150 cells have been drawn and studied. As the 

 nervous system is the most actively growing of all the regions of 

 the body the majority of the cells studied have naturally been 

 found in some part of it. Cells with clear polar views of meta- 

 phase chromosomes have been found in the brain, neural tube, 



1 The observations recorded in this paper were made principally at the Universit y 

 of Pennsylvania during the writer's tenure of a National Research Council Fellow- 

 ship. 



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