248 (ionetic Interpretations in the Domain of Anatomy 



foundation of all our instruction in anatoni}', and that its importance 

 should be constantly emphasized in our chiss-rooms and that when good 

 illustrations of cytomorphosis are encountei-ed by the student, his atten- 

 tion should be especially directed to them, so that he may become familiar 

 with the conception. Let me mention a few illustrations which I have 

 found serviceable in teaching. 



But first I must call your attention to an aspect of cytomorphosis, which 

 has not hitherto, so far as my knowledge goes, been sufficiently empha- 

 zised. We may distinguish two fundamental phases. During the first, 

 cell division occurs, during the second, cell division does not occur. Dur- 

 ing the first phase we may find a progressive alteration, which gradually 

 takes place in successive generations of cells, but apparently the amount of 

 differentiation which can occur while cells retain the power of active 

 division is comparatively slight. During the second phase, since the cell 

 no longer divides, the alteration takes place in the single cell, and the 

 alteration, which occurs under these conditions, is typically great and may 

 be best designated by the term final differentiation, difl'erentiation being 

 here held in our minds clearly distinct from degeneration. By final 

 differentiation we mean the establishment of that special organization 

 of a cell, which brings to perfection the specialized physiological function 

 for which the cell is destined. Thus the alteration of a mesenchymal cell 

 into a muscle fibre is its final differentiation, and establishes the physi- 

 ological perfection of that cell as a contractile element. Beyond the 

 final differentiation of the cell comes the series of degenerative changes. 

 A comprehensive study of cell degeneration is yet to be made, nevertheless 

 we can already say that, although cell degeneration is chiefly character- 

 istic of the second phase of cytomorphosis, which is also characterized 

 by the cessation of cell division, yet the degeneration may be initiated 

 before the power of cell division is lost and the degenerative change in the 

 cells may go on while they are still proliferating; but topically it seems 

 rather that degeneration belongs to the second phase of cytomorphosis, 

 and this seems to be alike true for necrosis and atrophy, that is to say, 

 simple cell death, and for necrobiosis, that is to say, cell death preceded 

 by structural changes, which we know commonly under the name of 

 hypertrophic degeneration. 



Let us pass on now to a few illustrations of cytomorphosis: 



The first to which 1 would direct your attention is afforded by the 



formation of the " trophodenii." This is a new term which 1 have 



recently brought forward to designate the special layer of cells formed 



apparentlv from the ectoderm (or according to Assheton's theory, from 



