THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 95 



fact has not been given due emphasis, so far as I am aware, that this mitochondrial 

 substance which persists in the fully developed spermatozoon is very different from 

 the typical mitochondria occurring elsewhere. It is well known that the mitochon- 

 dria undergo definite chemical changes in the course of spermatogenesis. Regaud 

 (1910, p. 294) clearly showed that their resistance to acetic acid grows greater and 

 greater; in fact, the structures which they form, nebenkern and spiral filament, 

 were known and recognized long before the mitochondria in the earUer stages of 

 spermatogenesis were brought to hght. They can be stained by ordinary methods 

 of technique and are resistant to acetic acid. While it can not be denied that these 

 structures are actually developed from mitochrondria, it certainly requires a con- 

 siderable stretch of our definition of mitochondria to include them under the head- 

 ing of mitochondrial apparatus and to make the statement that mitochondrial 

 substance occurs in the fuUy developed spermatozoon. 



(3) That in many cases these mitochondrial products enter the egg on fertil- 

 ization. 



The observations of Aleves (19116, p. 709) on Ascaris megalocephala, confirmed 

 by Held (1912, p. 247), Romeis (19136, p. 166), and Faure-Fremiet (1913, p. 585); 

 those of Meves on Parechinus miliaris (1912, p. 102), Phallusia mamillata (1913, 

 p. 225), Filaria papillosa (19156, p. 58), and Mytilus edulis (1915c, p. 54); those of 

 Duesberg (1915, p. 41) on Ciona intestinalis; of Levi (1915, p. 488) on Vespertilio 

 murinus, and many others all show that this occurs. 



It is to be noted, furthermore, what a very comprehensive list of animals has 

 been studied which is representative of many of the great divisions of the animal 

 kingdom. It is indeed a body of evidence which can not be well evaded. A few 

 years ago derivatives of mitochondria were known to pass into the egg in only a 

 few instances. Now we reahze that they usually do so. 



(4) That these same mitochondrial products which enter the egg in this way 

 can be recognized up to a certain stage in the development of the resulting embryo. 



Thus Meves (1912, p. 116) followed them through the first and second divi- 

 sions of the fertiUzed egg. Faure-Fremiet (1913, p. 586) studied the fate of the 

 male mitochondria in Ascaris. Levi (1915, p. 523) traced them into a 3-blastomere 

 stage in the Fallopian tube. It can easily be seen by a careful study of the illustra- 

 tions presented by these authors, and it is important to note, that these substances 

 behave in every way Like foreign bodies; they undergo no changes and seem to 

 exercise no influence upon the behavior of the other formed elements in the cyto- 

 plasm. In this they may be contrasted sharply with chromatin. It would be 

 interesting to compare, with respect to mitochondria, the subsequent development 

 of eggs fertilized artificially with some fertiUzed with sperm in the usual way. 

 Jacques Loeb (1916, p. 316) has succeeded in rearing to sexual maturity frog 

 embryos which were artificially fertilized. An examination of mitochondria dur- 

 ing spermatogenesis in these forms might afford the most valuable information. 

 If the mitochondrial content of the sperms differed from those of ordinary frogs 

 it would be of the greatest significance from the point of view of whether or not 

 the mitochondria are heredity carriers, which is the central theme of most of the 

 recent studies on mitochondria. 



