THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 99 



though they contained no mitochondria, nevertheless appeared normal, from 

 which she concludes that mitochondria are not necessary for differentiation. Dues- 

 berg (1915, p. 67) very aptly remarks that these experiments do not show that 

 mitochondria do not play a role in the differentiation of tissues, because no tissues 

 at this stage have yet become differentiated. He is not incUned to accept Beck- 

 with's statement that mitochondria are absent in the early stages of oogenesis and 

 that they do not appear until the vitellus is well formed (they form, Beckwith 

 behaves, de novo in the cytoplasm), which is totally at variance with all we think 

 we know of the mitochondria in oogenesis, as well as being in contradiction to the 

 observations of Tsukaguchi (1914, p. 117) on Aurelia aurita, an animal belonging 

 to the same class as Hydractinea echinata. 



The greatest obstacle to the acceptance of the view proi)ounded by Benda 

 and Meves is our conception of the chemical nature of mitochondria. If it is true 

 that they are phosphohpins it is hard to regard them as carriers of heredity, even 

 though they may contain albumin also. It can not be denied that, chemically, 

 chromatin appears to be the best htted to play the part of heredity carrier. The 

 relative equality in the amount of chromatin between the male and female gametes 

 and the deficiency in the amount of the cytoplasm must mean something. Even 

 should it be shown that mitochondrial substance passes over in fertilization in all 

 animals, it may indicate nothing more than that a living portion of the sperm, 

 capable of metabohsm, enters the egg. It is a mistake, however, to arrive at a 

 hasty conclusion, because those who make the conservative statement that mito- 

 chondria play some part in heredity occupy just as secure a position as those, on 

 the other hand, who claim that chromatin is the sole heredity carrier. 



In the higher plants it is well known that all the cells of the gametophyte 

 contain the x number of chromosomes and the cells of the sporophyte, or sexless 

 generation, contain the double number 2x, yet no distinction has been shown in 

 the mitochondria, which appear similar in every particular. Fvu-thermore, in the 

 aphides, or plant lice, there is also an alternation of generations, but a compari- 

 son of the mitochondria in the two has not been made. 



ORGAN-FORMING SUBSTANCES. 



Recent investigations on mitochondria in the early stages of the development 

 of Ascaris (Faure-Fremiet, 1913, p. 676) and of ascidians (Duesberg, 1915, p. 66) 

 throw a flood of new light upon our conception of the so-called "organ-forming sub- 

 stances" (Conkhn, 1905, p. 216). 



Conklin (1905, p. 211) has discovered the fact that the cytoplasm of the egg 

 of Cynthia is structurally differentiated into three substances — a clear substance, 

 a yellow substance containing yellow pigment, and a gray substance containing 

 yolk; and that "the upper clear half of the egg gives rise to ectoderm; the cres- 

 cent of yellow jirotoplasm surrounds the posterior side of the egg just below the 

 equator and is later transformed into the muscle and mesenchyme of the larva; 

 the gray protoplasm occupies the remainder of the lower hemisphere and gives 



