45 ELMER L. SHAFFER. 



important, if as yet unknown part in the history of fat meta- 

 bolism" (p. 172). 



Some workers (Kingsbury, '12, Cowdry, '17, etc.) have ex- 

 expressed the view that the mitochondria are concerned in the 

 processes of cell-respiration, but there has not been sufficient 

 experimental work to support this view. Maclean ('18) points 

 out some very interesting relations between lipins and oxydative 

 processes and mentions the work of Stanewitch who found that 

 wheat embryos treated with solvents which extracted most of 

 the lipins showed a respiration energy which was lower than 

 normal. 



It would, I think, be premature to make any definite statement 

 as to the function or significance of the mitochondria in organisms 

 until we know more of the biological significance of the lipins. 

 Maclean says (p. 107): 



"From what has already been said regarding the unsatis- 

 factory state of our knowledge of the lipins, it follows that their 

 exact function in the animal and vegetable economy is neces- 

 sarily obscure. Their great importance is proved by their 

 general occurrence in every cell, but little or no direct experi- 

 mental proof indicating their specific function has yet been 

 obtained. When we consider the obscurity in which the chem- 

 istry of the lipins has been shrouded and the fact that even now, 

 in many cases, is not satisfactorily established, it is easy to 

 understand that many of the properties and functions ascribed 

 to these bodies are based on little more than the imagination." 



For the present, all we can say regarding the function of the 

 mitochondria is that they form the major part of the lipoid 

 constitution of organic cells, and when we know more of the 

 biological significance of lipins, we shall know more concerning 

 the role of the mitochondria in cell economy. Obviously, further 

 progress in this direction must come along experimental lines. 



F. SUMMARY. 



1. The chromosome number in all male diploid groups of 

 Cicada (Tibicen) septemdecim is 19, and in the female diploid 

 groups 20. 



2. The diploid chromosome groups are characterized by the 



