16 E. V. COWDRY 



in the processes. No sickle-shaped bodies were seen. The pig- 

 ment is just as abundant in the small cells as in the large ones. 

 No relationship was observed between the pigment and mito- 

 chondria, although I would not deny that such may exist. 



DISCUSSION 



The analysis of the literature and the observations which I 

 have recorded show that mitochondria occur in the nerve cells 

 of representative examples of the chief vertebrate groups. Their 

 properties are so constant that the spinal ganglion cells of man 

 cannot be distinguished from those of any of the other forms, 

 which I have studied, on the basis of their mitochondrial content. 



A similar condition prevails in the developing nerve cell, in 

 which I have found mitochondria in stages from chick embryos, 

 before the differentiation of any somites, to adult fowls. My 

 series consists, in addition to the embryos already described 

 (Cowdry '14 a, p. 397), of preparations of four-day embryos, 

 of chicks just hatched and adult fowls. Unfortunately the later 

 stages are not very close together, but the series, as a whole, 

 is sufficiently complete to show that the relative amount, micro- 

 chemical properties and arrangement of mitochondria are approxi- 

 mately constant, although their morphology changes progres- 

 sively. In the spinal ganglion cells of a 35-somite chick, for 

 example, their average length is from 3 to 5m, but in the spinal 

 ganglion cells of an adult fowl they are seldom more than l^t 

 in length. These measurements were made on fixed and stained 

 material. 



I believe that this constancy of mitochondria in the phylogeny 

 and ontogeny of the nerve cell is significant, for it may serve 

 as a clue to their function. Their presence, the constancy of their 

 microchemical properties, relative amount and distribution within 

 the cell in the different stages of evolution and development may, 

 perhaps, be explained on the supposition that their function is 

 common to these same stages. It must be, therefore, a funda- 

 mental and a basic function, inseparably connected with the 

 life of the cell and subject, of course, to qualitative as well as 



