[CAMERON] VERTEBRATE STRIATED MUSCLE 97 



13. Each "line of chromatisation" is not a continuous one, but 

 is interrupted in the most definite and characteristic manner into 

 alternate achromatic and chromatic elements forming the rudiment 

 of a muscle fibril, and at the same time constituting the basis of 

 muscle striation. 



14. The muscle fibrils, of course, increase in number, as more and 

 more lines of chromatisation become produced. They are always 

 developed in groups, each forming the rudiment of a muscle fibre. 



15. The muscle fibrils increase in size as well as in number. 

 F.ach individual fibril becomes thickened owing to the gradual spread 

 of the chromatisation process from it into the surrounding undiffer- 

 entiated material. 



16. As development proceeds this undifferentiated material 

 becomes so encroached upon by the growing bundles of fibrils, that it 

 merely comes to form a thin zone enclosing each bundle and also 

 separating the individual fibrils, and likewise surrounding the nuclei. 



17. The "Bowman's elements" of the fibrils are each composed 

 at first of two "points of chromatisation", which become transformed 

 later into a dumbell-shaped structure, owing to the process of chromati- 

 sation extending slightly into the clear zone between the two "points." 



18. The constricted portions of the "dumbells" in neighbouring 

 fibrils are always placed alongside one another and the comparatively 

 clear line running across these forms the line of Hensen. 



19. In each muscle fibril a minute dot of chromatic material 

 makes its appearance in the centres of the clear spaces between the 

 elements of Bowman and at a slightly later period of development. 

 A similar dotted arrangement appears simultaneously in neighbouring 

 fibrils, the result being the production of Dobie's line. 



20. These conclusions on the mode of the production of muscle 

 fibrillae are utterly different from those of Godlewski who describes 

 in the myoblasts of the rabbit embryo the presence of isolated granules 

 which later arrange themselves in rows to form the primitive fibrillse. 

 In all the vertebrate types examined by the writer the fibrillation was 

 found to be definitely due to the chromatisation of a previously un- 

 differentiated material along definite lines of direction. 



21. The degenerative changes described by various investigators 

 in developing muscle tissue are probably explained by the remarkable 

 train of cytological phenomena described in Part IV of this memoir. 

 The writer was certainly unable to discover any signs of degeneration 

 in the vertebrate types examined by him. 



22. The results arrived at regarding the development of the 

 sarcolemma are likewise diametrically opposed to current opinions 

 on the subject. It appears comparatively late in development, and is 



Sec. IV, Sig. 7 



