100 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



rise to the endoderm, to the chorda, and to the neural plate." So much for the 

 fate of the "ectoplasm," the "mesoplasm," and the "endoplasm," as he styles 

 them. That these substances form the organs in question Conklin (p. 217) has 

 shown lieyond the shadow of a doubt. In the absence of one of the substances, 

 the organ to which it would naturally give rise is not produced; conversely, each 

 substance develops, if it develops at all, into the i^arts which it would normally 

 produce. The portions of the egg which lack these substances form embryos 

 which lack the corresponding organs. From these three fundamental substances 

 he derives six (p. 218), viz, ectoplasm, endoplasm, myoplasm, chymoplasm, caudal 

 chymoplasm, and chordaneuroplasm. 



Due.sberg (1915, p. 35) attacked the same problem in Ciona with new methods 

 which revealed the mitochondria and which showed that they occur in very differ- 

 ent amounts in the areas of cytoplasm described by Conklin. In the light of his 

 work it is evident that the myoplasm of ConkUn is simply an accumulation of 

 mitochondria, the gray protoplasm a region whose vitelline granules are particu- 

 larly numerous, and, lastly, the clear protoplasm nothing else than the fundamental 

 ground-substance of the egg, which contains but few mitochondria. Duesberg's 

 observations confirm the discoveries of Conklin as well as extend them. He found 

 that the areas form just exactly the organs which Conklin affirmed — that the yel- 

 low crescent which contains many mitochondria forms muscle, etc. But he does 

 not agree with Conklin's interpretation. To repeat, Conklin believes (p. 211) that 

 "all the principal organs of the larva in their definitive positions and proportions 

 are here marked out in the two-cell stage by distinct kinds of protoplasm." Dues- 

 berg (p. 60), on the other hand, is of the opinion that the different substances 

 in which Conklin believes do not exist. "The different appearances of different 

 regions of the egg and of the blastomeres depend not upon the existence of special 

 substances, but upon a special distribution of the elements figured in the ovoplasm, " 

 that is to say, of mitochondria, vitellus, pigment, etc. In other words, the regions 

 differ only in containing different proportions of the same substances ; none of them 

 possesses a special kind of substance. This interpretation, which I thoroughly 

 believe in, is also in accord with ConkUn's own observations. He writes (p. 212) : 



"Although these different ooplasmic substances are chiefly locahzed in certain regions 

 of the egg, which give rise to certain portions of the embryo, this segregation is not quite 

 complete. Most of the clear protoplasm is found in the upper (ectodermal) half of the 

 egg, but some of it is also present in the lower half. Most of the yolk is found in the lower 

 (endodermal) half of the egg, but a little of it is found in the upper half. Almost all of the 

 yellow protoplasm is located in the mesodermal crescent, but a very small amount of it 

 is found around the nuclei of all the cells. Thus samples of these egg-substances are con- 

 tained in all the cells; nevertheless the segregation is so nearly complete that the clear, 

 the gray, the light gray and the yellow areas are marked out with the greatest distinctness." 



Apparently there is a distinct relationship betwen the amount of mitochondria 

 and the amount of vitellus. For instance, the mitochondria are tremendously 

 abundant in muscle-cells and the vitelline granules few in number; in nerve-cells a 

 fair amount of both is present; while in the endodermal cells there is an enormous 



