130 



ALAN C. SUTTON 



N^-^- ll^ZX 



Fig. 4 Sensoiy endings in a 17 mm. pig embryo. Numerous placques can be 

 seen on the myoblasts. They are shown in gray, intimately connected to the 

 neurofibrils. (Obj. Leitz, 1/12 oil immersion; ocular 4). 



Fig. 5 A sensory ending in a 25 mm. pig embryo including three muscle 

 fibers. A single myoblast, some of which still remain, is shown in outline to the 

 right. (Obj. Leitz, 1/12 oil immersion; ocular 4.) 



In the 17 mm. embryos the endings show a definite change. 

 Here for the first time we get, in addition to the nerve upon the 

 myoblast, a placque (which I have drawn in gray; fig. 4) that 

 extends along the fibril upon the surface of the muscle cell. In 

 the fixed tissue it stains a dull violet in contrast with the green- 

 ish-yellow muscle cell and is paler than the rich violet color 

 of the neurofibrils, which can be made out distinctly upon the 

 placque, as plainly as in the figures. In the fresh muscle, where 

 the nerve is bright blue, the placque is not so well seen, since 

 there is not so much contrast between the two shades of blue 



