[CAMERON] VERTEBRATE STRIATED MUSCLE 91 



(Figs. 5 and 6) and finally becomes discharged as nascent endoplasm. 

 leaving some of the nuclei in a remarkably collapsed condition. These 

 alternating phases of turgidity and collapse of the nuclei are of course 

 constantly going on. The result of this discharge is to increase 

 enormously the amount of perinuclear material, which is thus for the 

 most part composed of an entirely new substance ready to undergo 

 fibrillation and form muscle fibrils. This brings me to the point of 

 mentioning and also emphasising the existence of two very distinct 

 phases in myo-genesis, which have not been previously described, 

 namely, a nascent or achromatic and a more mature ov fibrillar phase. 

 I have already demonstrated in several papers the existence of these 

 two important phases in the histogenesis of nerve fibres.^ 



VI. Stage of "Fibrillation." 



The study of the stage of fibrillation of the myo-syncytium 

 proved a most interesting and instructive one. The very earliest 

 signs as shown in Figs. 6 and 9 were found to be in the form of minute 

 dots placed in definite longitudinal rows. The size of these tiny 

 specks is such that they are capable of being successfully studied 

 only by means of the highest powers of the microscope, the 1-12 oil 

 immersion lens being the most suitable for this purpose. As they 

 were found to be relatively larger in lower vertebrate types, they 

 were most favourably studied in these. It may be noted, however, 

 that their appearance and mode of development are exactly the same 

 in higher vertebrates. Some idea of the size of these dots may be 

 gained from the fact that, when experimenting with the various 

 staining agents it was found that eosine which is supposed to be one 

 of the best stains for adult striated muscle, showed up developing 

 fibrils either imperfectly, or not at all, in the stage represented by 

 Fig. 9, whereas my modification of the iron-alum-haematoxylin stain 

 demonstrated their existence successfully as this figure shows. Be- 

 sides, eosine was found to be a useless stain for microphotographie 

 purposes. 



To continue the study of these primitive muscle fibrils. Two 

 very important facts will be observed in Fig. 10. In the first place, 

 note that the dots of each fibril are arranged definitely in pairs, whilst 

 it will in addition be recognized that these pairs are invariably situated 

 alongside each other in the same bundle of fibrils. The result is of 

 course the production of the transverse striation, which is therefore 



iRrain, Vol. CXV, 1906. 



Studies from Anat. Department, Univ. of Manchester. Vol. Ill, 1906. 



Jour, of Anat. and Phys., Vol. XL, 1906. 



