[CAMERON] VERTEBRATE STRIATED MUSCLE 95 



muscle for the purpose of giving rise to the sarcolemma. In the 

 first place there are no separate muscle fibres between which such a 

 tissue could grow in the early stages of myogenesis, during which I 

 have described the existence of one continuous nucleated mass of 

 cytoplasm — the myo-syncytium. It is therefore difficult to imagine 

 how special mesenchyme could force its way through such a tissue. 



The most significant fact of all, however, is, that the sarco- 

 lemma makes its appearance simultaneously throughout the whole 

 muscle. This surely indicates that it is being produced i7t situ by a 

 differentiation of the zone of achromatic material still forming the 

 periphery of each group of muscle fibrils.^ This is illustrated in Figs. 

 13 and 14 which are both transverse sections. Fig. 13 shows groups 

 of muscle fibrils each consisting of a considerable number, and yet 

 there is no sign of formation of sarcolemma tissue. In the later 

 stages, on the other hand, the number of fibrils has so enormously 

 increased as to leave merely a narrow clear zone surrounding each 

 group. Fig. 14 shows this undifferentiated zone in process of trans- 

 formation into supporting fibrous tissue, within which some of the 

 original nuclei of the myo-syncytium are being included to form 

 sarcolemma nuclei. Dr. Gladstone and the writer- have already 

 pointed out that the histogenesis of any kind of tissue is essentially a 

 question of differentiation of the general syncytial mass which con- 

 stitutes the embryo during the early stages of development. From 

 this standpoint it is easy to understand how the individual muscle 

 fibres are produced. These are simply bundles of fibrils which at a 

 certain stage of development become mapped off from their neigh- 

 bours, both in a transverse and in a longitudinal direction, by the 

 transformation of the peripheral zone of undifferentiated material 

 into sarcolemma tissue. I can thus find no evidence that the latter is 

 developed as an independent structure from special mesenchyme 

 connective tissue cell-elements. Moreover, I was able to ascertain 

 that the epi-peri and endo-mysium are like the sarcolemma, formed 

 by a further differentiation of those portions of the myo-syncytium 

 which do not become transformed into muscle fibrils. 



From what has been stated throughout this paper, it will now 

 be recognised that a muscle fibre has no developmental relationship 

 whatever to a single "cell". If any further evidence were required 

 to condemn the cell-theory, surelj^ the histogenesis of striated' muscle 

 supplies it in abundance. 



'Miss McGill has shown that in non-striated muscle the connective tissue arises 

 in situ (op. cit.) 

 20p. cit. 



