DEVELOPMENT OF THE ADRENALS IN THE TURTLE 85 



•them of numerous blood corpuscles. Wherever aggregates of 

 chromaffin cells are found in the cortical substance they occur in 

 or adjacent to such spaces. It is probable, therefore, that chro- 

 maffin cells penetrate into the cortical substance only in these 

 vascular spaces. 



It may be noted at this point that not all the elements which 

 • become differentiated into chromaffin cells ever become incorpor- 

 ated into the adrenal organs. During the later stages of develop- 

 ment in embryos of Thalassochelys caretta aggregates of these 

 cells may be found entirely apart from the adrenals. In Chryse- 

 mys marginata, in the adult condition, I have also observed aggre- 

 gates of chromaffin cells associated with the sympathetic ganglia 

 in proximity with the adrenals. Similar conditions were observed 

 by Poll in Emys europaea and by some of the earlier investigators 

 in various species of other classes of vertebrates. 



GENETIC RELATIONSHIP AND DIFFERENTIATION OF CHROMAFFIN 



CELLS 



In a series of earlier papers, 3 the writer has shown, for the 

 several classes of vertebrates, that the cells which become sepa- 

 rated from the cerebro-spinal nervous system and advance periph- 

 erally to give rise to the sympathetic nervous system are the 

 descendants of the 'germinal' cells (Keimzellen) of His; viz., the 

 indifferent' cells and the 'neuroblasts' of Schaper. The vast 

 majority of these cells (in the lower vertebrates perhaps all of 

 them) advance peripherally as cells of the 'indifferent' type. 

 These cells have the capacity of becoming differentiated into 

 neuroblasts or into embryonic supporting cells. Some of the 

 'indifferent' cells, however, retain the capacity for further propa- 

 gation by division and give rise to new generations of 'indifferent' 

 cells after they have become separated from the cerebro-spinal 

 nervous system. 



As indicated in an earlier section of this paper, the cells which 

 become separated from the sympathetic anlagen and enter the 

 anlagen of the adrenals there to give rise to the chromaffin sub- 



3 See bibliography. 



