[CAMERON] VERTEBRATE STRIATED MUSCLE 85 



of development the characteristic appearance of a syncytium with 

 fibrils developed within it extending for considerable distances beyond 

 the limits of anything that could be possibly regarded as individual 

 cell-elements. 



One of the earliest signs of myo-genesis is a multiplication of the 

 nuclei of the myo-syncytium, a phenomenon which is freely recognized 

 by embryologists' and is as readily substantiated. A closer study, and 

 more intimate acquaintanceship with these nuclei, however, disclosed 

 a rather strange behaviour which I have not seen previously chronicled. 

 For example it was noticed that some were of an enormous size, and 

 looked pale and turgid, whilst others in the neighbourhood appeared 

 quite collapsed and shrunken (see a, a' and b, b' in Fig. 2). After 

 various experiments I found this appearance was not due to faulty 

 fixation, and, moreover, it was seen to best advantage in tissue which 

 had been fixed in the living state. Indeed, the latter condition was 

 found to be a sine qua non for the successful study of the phenomenon. 

 At the same time I noticed that the cytoplasm surrounding these 

 nuclei became enormously increased in amount, the result being a 

 transformation of the previous scanty mesenchyme network (Fig. 9) 

 into broad anastomosing columns of pale, feebly staining protoplasm 

 (Fig. 5 and 6). The shrinkage or collapse of the nuclei, and the 

 increased volume of the surrounding cytoplasm appeared to be two 

 very intimately associated phenomena, which suggested, at least, 

 that the nuclei, after becoming quite turgid, were discharging a part 

 of their contents to build up the cytoplasmic material. I made a pro- 

 longed study of these nuclei particularly in Amphibian types and was 

 successful in fixing several specimens just in the process of extruding 

 their fluid contents. The latter material at its first discharge, that 

 is to say, while in the nascent condition, is comparatively achromatic 

 in its behaviour towards iron-alum-haematoxylin and other staining 

 agents, so that its representation in a microphotograph presents 

 great difficulties. Fig. 3, however, shows a nucleus in the process of 

 discharging its achromatic material. On one side the nuclear "mem- 

 brane" is seen in a condition of collapse, while just outside this point 

 is a pool of achromatic fluid substance which can be traced in an up- 

 ward direction around the nucleus as a very narrow but definite clear 

 zone, which is in its turn continuous with a much larger and more 

 clearly outlined pool, slightly constricted near its junction with the 

 nucleus. A key diagram (Fig. 4) is appended to show the extent and 

 relations of this veritable reservoir of achromatic material, as Fig. 3, 

 though a successful microphotograph, does not do full justice to the 

 actual specimen. I may perhaps be permitted to state here that 

 the discussion of these complex cytological problems ought to be 



