[CAMERON] NEUROBLAST-NUCLEI - 5 



nuclear layers, however, would prolong this paper unduly. It will, 

 therefore, have to be reserved for a future communication. 



It is likewise interesting to note the alteration in the shape of all 

 the retinal neuroblast-nuclei during development. In the early 

 stages, as the Figs, show, these are consistently bipolar in character, 

 but by the thirty-fifth day they have assumed the rounded or spherical 

 shape of the adult (Fig. 5). The most satisfactory explanation of this 

 phenomenon appears to be that during the earlier developmental 

 stages, when the metabolic activity of these nuclei is probably at 

 its maximum, their achromatic contents are discharged from their 

 poles. This, by a simple problem in dynamics, would compel them 

 to assume a bipolar outline. During the later and probably less 

 active stages of histogenesis the nuclear metabolized material is 

 discharged at all points in the periphery of the nucleus, which would 

 render it physically incapable of assuming a shape other than that of 

 a sphere. At least this is the explanation which, in the light of our 

 present knowledge, suggests itself with most emphasis to the writer. 



The biological problems involved in this research are so diverse 

 and far reaching in character that it is impossible to do full justice to 

 them in this short paper, wbich will, therefore, require to be regarded 

 as a preliminary communication. 



Literature Cited 



(1) Cameron, John, The development of the retina in amphibia, Jour, of AnaL, 1905 



(2) Cameron, J., and Gladstone, R. J., The structure of the Blastoderm, Ibid. 1916. 



(3) Cameron, John, The histogenesis of striated muscle, Trans. Royal Soc. Canada, 



1917. 



(4) Detwiler, S. R., Jour, of Experimental Zoology, Feb. 1916. 



(5) Bernard, H. M., Studies in the retina, Quart. Jour. Micros. Science, Vols. 43 to 47. 



(6) Cameron, John, The development of the vertebrate nerve cell, Brain, 1906. 



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