CYTOPLASMIC CONSTITUENTS OF NERVE CELLS 409 



2. Criticism of the theory 



The material and methods wpon which the statements are based. 

 In many cases the embryological series have been made up of 

 embryos of different types of animals. It is a well-known fact 

 that similar portions, of the nervous system of different animals 

 are often not differentiated at the same rate, so that comparisons 

 made in a heterogeneous series are not vaUd. I know of no in- 

 vestigator who has clearly and concisely described either the ex- 

 tent or the composition of his series of embryos. The criteria 

 used for the characterization of the different developmental 

 stages have been lamentably deficient. Every biologist knows 

 that embryos of apparently the same period of incubation may 

 differ widely in their degree of differentiation. This is particu- 

 larly true in the case of eggs which have been bought from 

 dealers and about which we consequently know but little. 



Complete series, cut in transverse, sagittal and coronal planes, 

 have not, as a rule been studied; and care has not been taken, 

 in forming a synthetic picture of the cytoplasmic constituents, 

 to draw material only from strictly homologous cells (Herrick '09) 

 of the same degree of differentiation. Few methods of technique 

 have as a rule been taken advantage of, and, in some instances, 

 conclusions have been deduced solely from the application of a 

 single method. In the majority of investigations no reference is 

 made to the use of subsidiary methods designed for the control 

 of the finer form relations, and resort has never been made to 

 vital dyes. 



The statements. (1) My own observations are utterly at vari- 

 ance with the first argument, for I find that there is no decrease 

 in mitochondria running parallel to the formation of neurofibrils. 

 Moreover the statement that mitochondria are absent in the 

 adult condition is wholly unwarranted in view of the fact that 

 several investigators have unquestionably demonstrated mito- 

 chondria in adult nerve cells. Altmann, as far back as 1890, 

 described and figured them in spinal ganglion cells of the frog 

 (fig. 2), and in the Purkinje cells of the cerebellum of the cat (fig. 

 3) as well as in the brain wall and in the medullary tube of cat 



