PLATE 3 



EXPLANATION OF FIGURES 



Plates 3 and 4 constitute the essential features of a comparison of the results 

 yielded by Meves' iron hematoxylin method and by Cajal's silver nitrate tech- 

 nique respectively. In both cases drawings have only been made from sections 

 of the neural tube on the right side opposite the sixth somite and the degree of 

 differentiation of the embryos from which the figures of plate 3 were drawn cor- 

 responds severally with that of those represented on plate 4 (fig. 15 a to fig. 15 b 

 and so on). The drawings have been arranged so that the membrana limitans 

 externa is to the left hand side of the observer. A collation is therefore justified 

 since morphologic equivalents of approximately the same area and thickness 

 (4/i) are only being used. This comparison of homologous equivalents in increas- 

 ing stages of development prepared by these two methods, the one showing mi- 

 tochondria, the other neurofibrils, indicates: (1) That there is no decrease in the 

 amount of mitochondria parallel to the increase in neurofibrils. (2) That the 

 mitochondria do not show, either by a variation in their morphology, staining 

 reactions, or in any other way, capable of being detected by our present-day 

 methods, indications of being transformed into material of radically different 

 chemical composition (pp. 407 and 416.). 



15 a From the right side of the neural tube in the region of the sixth somite 

 of an embryo of 17 somites, length 5.5 mm. and incubation forty-five hours. The 

 mitochondria are filamentous, their irregular shape, as seen in the drawings, de- 

 pends upon the fact that their long axes are directed in all planes relative to the 

 drawing and that they are cut in pieces of many sizes, at all angles during sec- 

 tioning. There is a remarkable variation in the color of the back-ground, for in 

 two cells, (a) and (b), the cytoplasm remains practically unstained, although 

 there is apparently no other difference between them and the neighboring cells 

 (p. 408). 



16 a Same region, embryo of 20 somites, sixty-two hours incubation. There 

 is no change in the mitochondria. 



17 a Same region, embryo of 22 somites, fifty-two hours incubation. The 

 section has been cut rather obliquely. There is no change in the mitochondria. 



18 a Same region, embryo of 24 somites, length 7.0 mm. and sixty hours in- 

 cubation. The section is even more oblique. The mitochondria show no change. 



19 a Same region, embryo of 28 somites, sixty-four hours incubation. No 

 change in mitochondria. 



20 a Same region, embryo of 31 somites, seventy hours incubation. There is 

 still no change in the mitochondria. 



424 



