94 THE ROYAL SOCIETY OF CANADA 



second place it is difficult to imagine such minute dots as having the 

 dimensions worthy of an area. 



So much for the increase in number of the fibrils. They also 

 increase in size at the same time. This is very well demonstrated 

 in Figs. 11 and 12 which are from Zoarces embryos, 28 m.m. and 

 48 m.m. in length respectively, and show the same degree of magnifica- 

 tion. It will be noted in Fig. 12 that the individual fibrils have greatly 

 increased in thickness owing to the gradual spread of the chromatisa- 

 tion process into the surrounding undifferentiated material. It will 

 likewise be observed both in Figs. 11 and 12 that the earliest formed 

 fibrils (i.e. those round the periphery) are much thicker than the more 

 recently formed ones in the centre. Figs. 12 and 14 show how little 

 of the primary achromatic material is left, owing to the great en- 

 croachment of the fibrils upon it. What remains merely forms a thin 

 zone, separating the individual fibrils, a condition which of course 

 persists in the adult. The undifferentiated material is, however, 

 still found in greatest abundance around the nuclei, as is well demon- 

 strated in one of the bundles of fibrils shown in Fig. 12. 



Godlewski^ describes in the myoblasts of the rabbit-embryo 

 the presence of isolated granules which later arrange themselves in 

 rows to form the primitive fibrillse, while Meves^ and Duesberg^ 

 likewise refer to the existence of granules or "mitochondria" in myo- 

 blastic tissue, which presently dispose themselves in longitudinal 

 series along one side of the developing muscle fibre. My conclusions 

 are utterly different from these, for in all the types that were examined 

 by me (and these, I may add, represented every vertebrate class) 

 the fibrillation was found to be definitely due to the chromatisation 

 along definite lines of a previously undifferentiated material. The 

 latter possesses the fine "granular" appearance of ordinary cyto- 

 plasm, but I could discover no isolated granules which would be free 

 to migrate from one part of a cell body to another and arrange them- 

 selves in rows. The recognition of the achromatic and chromatised 

 phases of fibrogenesis provides therefore the key to the whole problem. 



VIII. The Development of The Sarcolemma. 



The sarcolemma is comparatively late in making its appearance. 

 I could find no evidence of its development during the early stages, 

 as some authorities declare. The results of my observations on its 

 mode of formation are likewise diametrically opposed to the current 

 opinions on the subject. For example, I was unable to discover any 

 evidence of an ingrowth of mesenchyme tissue into developing striated 



\^ &\ Anat. Anzeiger, Bd. xxxiv, 1909. 



