[CAMERON] VERTEBRATE STRIATED MUSCLE 89 



Amphibian retina, and at about the same time. They are thereby trans- 

 formed into clear globules which consist of the yolk granules dissolved 

 in this nascent achromatic material which is possibly discharged from 

 the nuclei. It is a very significant fact, that the yolk-granules lying 

 free in the interstices of the cytoplasmic network and those embedded 

 in the myo-syncytium itself are simultaneously attacked and digested. 

 Indeed the cytoplasm of the myo-syncytium is so excessively scant\' 

 in the early stages that the majority of the yolk-granules appear to lie 

 free in the surrounding tissues. Again, if the yolk particles were 

 digested by the cytoplasm itself one would expect them to become 

 attacked before the 19th day. The above circumstantial evidence 

 seems to point to the fact that this digestive agent is a newly formed 

 substance, possibly nuclear in origin, as previously demonstrated by 

 the writer in embryonic nerve tissue.' It should also be pointed out 

 that Dr. Gladstone and the author'^ have shown that the nascent 

 endoplasm which is the active constituent of cell protoplasm is a 

 derivative of the metabolic activity of the cell-nuclei. The possible 

 origin of this enzyme substance from the cytoplasm itself is however 

 not entirely put out of court. By the 23rd day (Fig. 3) practically 

 the whole of these yolk granules have become transformed into 

 globules and merged in the general protoplasmic mass. 'In Figs. 

 3, 5 and 6 traces of the disintegrated yolk can still be observed here 

 and there in the form of minute globules. The nucleated mass of 

 protoplasm shown in Fig. 5 which is now prepared for the formation 

 within it of muscle fibrils, may thus be not inaptly termed the myo- 

 syncytium. 



This investigation of the earliest phases of myo-genesis thus 

 yielded cytological results far beyond any I had dreamt of, and it 

 provides an important contribution to our knowledge regarding the 

 functions of the cell-nucleus. The word "energid" is one which has 

 come very much to the forefront lately; but this term has been so 

 loosely applied that I referred to the American Illustrated Medical 

 Dictionary for its definition, which is — "the nucleus and its active 

 cytoplasm, regarded as the essential living part of the cell." From 

 this definition I gather that the cytoplasm referred to is the zone of 

 active endoplasm immediately surrounding the cell-nucleus, described 

 by Dr. Gladstone and myself. However, it is clear not only from the 

 present investigation, but also from previous research by the writer 

 on the embryonic retina^ and developing nerve tissue,^ and likewise 



iQp. cit. 

 20p. cit. 

 30p. cit. 

 ^Brain, Vol. CXV, 1906. 



