132 ALAN C. SUTTOX 



elsewhere, though this is not an infalhble rule. While the end- 

 ings are, in the majority of instances, somewhere near the middle 

 of the fibers, I have seen, at various times, endings in which the 

 terminal net bound together two muscle fibers where they came 

 together, end on. I think the nerve can attach itself at any 

 point along the fiber. When union takes place in the myoblastic 

 stage, as the cell grows the ending is left near the middle of the 

 fiber. The spindles, which enclose the ends of muscle cells, 

 have most likely included these fibers later within the terminal 

 plexus. Not all the intrafusal fibers became a part of the spindle 

 in the myoblastic stage. This seems to be the case in figure 8, 

 where the ending upon the outer fiber is of the very simplest 

 type. But no more muscle cells are added after the 200 mm. 

 stage, for by this time the entire ending is enclosed in a definite 

 connective tissue sheath. At this stage, where a few myo- 

 blasts still persist (in fact, they do not disappear altogether 

 until 170 mm. — Bardeen) it is not unconnnon to see them in- 

 cluded in an ending with the more advanced muscle fibers (fig. 

 6). These cells do not all grow at the same rate. Just what 

 is the determining factor is not known. The future historj^ of 

 the muscle cell seems to some extent to be dependent upon the 

 neural connection. Bardeen ('02) says: 



It seems probable the sarcolemma is formed through the action of 

 sm'face nuclei of the muscle fiber, in response, probably, to stimuli 

 arising from the union of the nerve with muscle fiber ; and it is so formed 

 as to enclose that portion of the nerve which is spread out over the pro- 

 toplasm of the muscle. 



This is also suggested by the degenerative changes in many 

 of the fibers later on in embryonic life. In any of the embryos 

 longer than 75 mm., many muscle fibers can be seen which seem 

 to be breaking up into irregular masses of protoplasm and nuclei. 

 They also show an increase in the amount of intracellular pigment. 

 With the methylene blue stain they are filled with many droplets 

 which take up the blue stain. Bardeen ('00) regards this as a 

 ' retrograde metamorphosis.' Perhaps the cells develop slowly up 

 to a certain point and then, if there is no nerve connection es- 

 tablished, they degenerate. If a ner^ e connection is necessary 



