294 Changes in the Muscle Cell of Necturus 



shown in transverse section. These surface serrations were first observed 

 by Weber, 74, 489, in the nuclei of the muscle fibres of the frog and 

 correctly interpreted as the result of pressure from the muscle fibrillse. 



I was later gratified to find that Macallum, 87, had previously studied 

 the nuclear membrane in these particular nuclei. The nuclei were 

 isolated from the luuscle fibre of the adult Necturus Ijy macerating in 

 formic acid and then stained in gold chloride. By this method Macallum 

 was able to demonstrate both a longitudinal and a transverse striation of 

 the nuclear membrane, which he attributed to the pressure of the fibrillge. 



The linin network is seen more distinctly in transverse sections (Figs. 

 42-60) than in the profile. Its meshes are smaller than in the 17-26 mm. 

 stages; in some sections large, irregular meshes are seen (Figs. 48, 55, 

 58), which are due to the rupture of a number of threads during prepa- 

 ration. The threads are finer than in the 17-26 mm. stages and show 

 decidedly less affinity for chromatic stains. Macallum says that " there is 

 in some nuclei a reticulum like in every respect to that found in muscle 

 substance." My studies, however, lead to the conclusion that the net- 

 work in the nucleus is entirely independent of that in the cytoplasm. 



Plasmosomes are always present, but in general are fewer than in the 

 6-15 mm. stages; most frequently they are distrilnited somewhat as in 

 Fig. 41. There is no marked sheath of chromatic granules around them 

 and their staining capacity is notably less than in the earlier stages. 



The karyosomes, as shown in the various figures in Plate IV, are re- 

 markably few in number when compared with any of the preceding 

 stages; they are smaller, usually lie wdthin the membrane, rarely if ever 

 uniting in a peripheral band. The most striking difference is their slight 

 affinity for nuclear stains. Macallum found many nuclei in which there 

 was no chromatin. Although I have made a careful examination of a 

 very large number of nuclei, I have never found one in which there was 

 no chromatin; it seems quite probable, however, that such may occur. 

 At any rate the important fact should be emphasized that one of the most 

 striking characters of the old nuclei is a great reduction in the amount 

 of chromatin. 



GENERAL DISCUSSION OF VARIOUS PROBLEMS IN MYOGENESIS. 



A. Concerning the Myoblasts as a Whole. 



ITS unicellular character, method of increase in number and 

 SIZE of the fibres, the sarcolemma. 



The revival by Godlewski of the older theory that the muscle fibre is 

 a multicellular structure, as first formulated by Valentine and Schwann, 



