90 THE ROYAL SOCIETY OF CANADA 



from recent results obtained by Dr. Gladstone and the writer^ on the 

 blastoderm, that the real centre of metabolic energy is the cell-nucleus. 

 It will therefore be necessary again to study step by step the various 

 phenomena chronicled above, and carefully analyze the results thus 

 yielded. In the first place it is evident that the yolk granules imbedded 

 in the myo-syncytium, are attacked and digested by some new potent 

 substance which is suddenly discharged into the tissues. The writer 

 pointed out many years ago that this was a nascent achromatic 

 material discharged probably from the cell-nuclei. As suggested 

 in previous communications this mysterious substance must there- 

 fore possess the properties of an unformed ferment or enzyme. The 

 digestion of the yolk granules of developing muscle is evidenced by the 

 fact that they become suddenly achromatic in their reaction to 

 staining agents, even though they may be lying free in the tissues, and 

 disappear altogether. Concomitantly with this disappearance the 

 cell-nuclei become enlarged, owing to the ingestion by them, of 

 some of the constituents, at least, of these digested yolk granules. 

 In the retina and other nerve tissue, the author has previously shown 

 in several communications that this ingestion takes place at a definite 

 pole of the neuroblast nucleus, to which h'e gave the name of assimil- 

 ative pole,"^ immediately inside which the ingested material is stored 

 up in the form of nuclear chromatin. It would appear, then, that 

 the final stages of ingestion of food material take place in the cell-nucleus. 

 This accumulation of deeply staining chromatic substance at one pole 

 of each neuroblast nucleus imparts a very characteristic appearance 

 to the cerebral wall of some of the lower vertebrate types at a certain 

 period of development. 



The turgid overloaded nuclei of the myo-syncytium instead of 

 this polar accumulation exhibit a general increase in the amount 

 of their chromatin element. There is, however, one very characteristic 

 and significant fact to be recorded regarding these nuclei in Amphibian 

 types. In this vertebrate class the nucleoli appear to be of particular 

 importance as storehouses of chromatin, and accordingly attain a 

 large size sometimes (see Fig. 6 and also Figs. 3, 5, 7, and 10). Accord- 

 ing to Schafer" "the nucleolus is usually regarded as a product of nu- 

 clear metabolism," a statement which is strongly substantiated by the 

 results of the present research. 



The next stage is very definite. This storehouse of nuclear 

 chromatin becomes partially retransformed into a fluid achromatic 

 substance which at first distends the nuclei to an enormous extent 



^Op. cit. 



2Brain, Vol. CXV, 1906. 



^Quain's Anatomy, 11th Edition. Histology Volume, p. 37. 



