CYTOPLASMIC CONSTITUENTS OF NERVE CELLS 401 



where the sections are cut in most instances transversely to the 

 length of the cells with the result that the mitochondria appear 

 either uniformly granular or as short rods depending upon the 

 thickness of the section in question. The preponderance of the 

 filamentous form of mitochondria may be conclusi\^ely demon- 

 strated in specimens stained with janus green intra"\'itam. 



The morphology and cytoplasmic arrangement of mitochondria 

 are represented in figures 2, 3, and 1, which illustrate progres- 

 i^ive stages in development. The specimens from which these 

 figures were drawn were prepared by Meves' modification of the 

 iron hematoxylin method so that the mitochondria appear a 

 dark blue-black color and may be readily distinguished from the 

 dark browinsh black yolk globules. The first (fig. 2) shows epi- 

 thelial cells from near the middle line of the medullary plate of 

 an embryo of twenty-four hours incubation at 39°C. in which 

 the primitive groove fold and pit alone were differentiated. The 

 mitpchondj'ia are seen in the form of filaments and granules dis- 

 tributed evenly throughout the cytoplasm, whereas the yolk 

 spherules show a tendency to become grouped together in the 

 distal, (i.e., remote from the membrana limitans interna) por- 

 tions of the cells. The second (fig. 3) illustrates the appearance 

 of epithelial and germinative cells from the neural fold in the 

 region of the head process of an embryo of 3 somites and twent}'- 

 four hours incubation. The amount of yolk material is reduced 

 and the mitochondria are far more abundant in the distal than 

 they are in the proximal parts of the cells. I have not, however, 

 been able to distinguish a similar heaping up of mitochondria 

 in cells stained by janus green intravitam (fig. 23). The third 

 drawing (fig. 1) is from the ventral half of the neural tube in the 

 region of the tenth somite of an embryo of 12 somites and thii-t}-- 

 four hours incubation. The mitochondria are here distributed 

 evenly in the cytoplasm and the yolk gloubules tend to be accu- 

 mulated in the distal portions of the cells, just as in figure 2. 



There are two points of considerable significance from the 

 point of ^'iew of the theory of the transformation of mitochondria 

 into neurofibrils. The first is that there is little, if siny, variation 

 in the morphology' or staining reactions of mitochondria in these 



