40 The Unity of the Organism 



back, that cytoplasm itself is hereditary substance, is Cow- 

 dry's detailed description of neurofibrils as a "differentia- 

 tion of the ground substance" of the neuroblasts. And in 

 a later paper the same author makes a strong case of the 

 view that while mitochondria are "associated in some way 

 with the formation of many substances," ^ it is highly im- 

 probable that they transform into them. 



On the whole the tendency of the latest investigations 

 appears to be to deny that the bodies produce, in a strict 

 sense, any tissue elements. Thus as a result of their quite 

 remarkable studies on mitochondria of living cells Lewis and 

 Lewis say, following the enumeration given above: "The 

 above theories seem impossible to correlate. It seems evi- 

 dent that the mitochondria are too universal in all kinds 

 of cells to have the function of forming any one of the 

 above structures of differentiated tissue, and in the light of 

 what cytological chemistry is known, it appears practically 

 impossible for the mitochondria to form all the cell struc- 

 tures mentioned above. In view of the fact that the mito- 

 chondria are found not only in almost all animal cells but 

 in plant cells as well it seems more probable that they play 

 a role in the more general physiology of the cell." ^ The 

 idea that the mitochondria are primarily concerned with the 

 metabolism of the cell appears to be gaining ground under 

 the present comprehensive and critical methods of investi- 

 gation that are being applied to them. 



The Untenable Hypothesis that the Cytoplasm of the Ovum 

 is Inheritance Material for General hut not for 



Special Characters 



A number of biologists have recently put forward the 

 hypothesis that while the cytoplasm of the egg-cell may be 

 "hereditary material" for certain of the general attributes 

 of the organisms, chromosomes "carry" the hereditary, 



