SPERMATOGENESIS OF PASSALUS CORNUTUS. 423 



The researches on the chemistry of mitochondria are prac- 

 tically all in agreement that they are phospholipins or lecithin- 

 albumins. No one has attempted to show that yolk is a bearer 

 of hereditary units; yet yolk is chemically allied to mitochondria. 

 In fact Faure-Fremiet has shown that mitochondria actually 

 transform into yolk. The work on the chemistry of mitochondria 

 indicates that they are of great importance in the metabolic 

 activity of cells, but our knowledge of their relation to heredity 

 is negative. To say that the mitochondria are not the bearers 

 of hereditary units is not denying that they may influence heredity 

 in some cases, just as we know that heredity can sometimes be 

 influenced by environmental conditions of food, temperature, etc. 



One fact which has come clearly to light from this study is 

 that beginning with the spermatogonia and continuing up to the 

 spermatid, there is a progressive elaboration of mitochondria. 

 They are then transformed into a definite structural part of the 

 spermatozoon, the sheath of the axial filament. This progressive 

 increase in the amount of mitochondria seems to indicate that 

 they are differentiation products. Hence if there is any genetic 

 continuity between the mitochondria of successive cell genera- 

 tions, it is only of a limited sort. The conception that the 

 mitochondria present in the somatic cells are the direct de- 

 scendants of those of the germ cells from which they have 

 arisen, certainly has very little evidence in its favor. It seems 

 more probable that mitochondria are in the nature of cyto- 

 plasmic differentiations, akin to metaplasm (yolk, etc.) and 

 without a definite relation to the development of hereditary 

 characters, but with the capabilities of influencing development 

 insofar as they may be related to the metabolic activity of cells. 

 It is possible that in the spermatozoa, the mitochondria merely 

 function as locomotory organs. 



SUMMARY. 



1. Although mitochondria can not be definitely demonstrated 

 in the primary spermatogonia of Passalus cornutus, they are 

 present in the secondary spermatogonia in the form of numerous 

 and diffusely spread granules. 



2. The mitochondria increase in number during the growth 



