THE NEURO-MUSCULAR SPINDLE 125 



except in the very earliest stages, in distinguishing the sensory 

 from the motor endings, as the sensory endings are from the very 

 first much more intricate. This can readily be seen in the 

 figures. ^Then too, the development of the motor endings has 

 been very thoroughly worked out by both Boecke ('10) and 

 Mays ('92). My findings of the motor endings were essentially 

 the same as theirs. 



V 



-JL 



Fig. 1 Three stages in the development of the motor end plate. The upper 

 drawing is from a o5 mm. pig embryo; the middle one from a 100 mm. ; the lower 

 from a 250 mm. embryo. The outlines of the individual muscle fibers are indi- 

 cated by straight lines. (Obj. Leitz, 1/12 oil immersion; ocular 4.) 



There is one disadvantage in the methylene blue method, 

 especially with the ammonium picrate fixative. It does not give 

 as distinct a picture of the muscle as one would like. However, 

 with the work of Bardeen ('00) on the development of the muscle 

 fiber in pig embryos, as a basis, I soon experienced little diffi- 

 culty in distinguishing the various types of muscle cells prior to 



