296 Changes in the ]\[usele Cell of Xecturus 



longituilinal splitting; this was advocated first by Eemak, 43, and more 

 recent]}^ by Felix, 88, and Godlewski, 02. 



In Necturns the increase in the number of muscle cells in the post- 

 aural myotomes proceeds at about the following rate : In the embryo of 

 10 mm. there are about 50 muscle cells; in the 15 mm., 150; in the 21 

 mm., 500 ; in the 26 mm., 1500. During these phases of rapid increase 

 the cells have been carefully and repeatedly examined with a view of 

 finding out whether or not a longitudinal splitting occurs. In no in- 

 stance have I found a myoblast undergoing division, nor have I found, 

 either in the position of the nuclei or in their direction of division, 

 any evidence that they participate in the division of the myoblasts. 



The increase in number is most pronounced at the dorsal and ventral 

 margins of the myotomes, yet new myoblasts are being formed on both 

 the lateral surfaces. The addition of new myoblasts is continued long 

 after the earlier formed muscle cells are fibrillated; in this respect the 

 condition in Necturus differs somewhat from that described by Mac- 

 Callum in the pig and man, in which the increase in the number of fibres 

 ceases at the time the first-formed myoblasts are fibrillated. The sole 

 method of increase between the 10 mm. and 26 mm. larva, so far as I 

 have been able to observe, is by the differentiation of new myoblasts 

 around the jjeriphery of the myotome. 



Eegarding the increase in size of the muscle cell, want of material pre- 

 cludes more than a preliminary statement. Up to and including the 

 26 mm. larva, there are no indications that an increase in size is brought 

 about through the lateral fusion of the myoblasts which, according to 

 Godlewski, does occur in the rabbit. The increase in size appears to be 

 due to the continued formation of the fibrillsB. As pointed out in a 

 preceding page, careful counts show that the number of fibrillse in the 

 ends of the myoblasts is greatly in excess of the number at the middle of 

 the myoblasts. That this is due to a longitudinal splitting rather than 

 new formation is supported by the fact that teased preparations show 

 many fibrillfe divided along a portion of their extent. Again, if new 

 formation plays any considerable part there would be found short filu'illas 

 without transverse markings, but such are not found. From these 

 observations, I am led to believe with Apathy, 92, Maurer, 94, and 

 Heidenhain, 99, that the increase in number of fibrillas is due to growth 

 and longitudinal division. 



Since its discovery by A^alentino the sarcolemma has been the subject 

 of repeated study. While much has l^een written there is as yet the widest 

 divergence of opinion. Schneider, 87, says it is an artifact. Wage- 



