Mitochondria, Golgi Apimratus, and Yolk. 139 



(2) yolk discs do not appear in the inner regions of the egg till 

 later, even though these regions may contain abundant mito- 

 chondria. 



It seems natural to conclude that the yolk grains of the egg 

 are formed from metamorphosed mitochondria, as is believed to 

 occur in other animals. It should be mentioned that in both 

 insects and amphibians the mitochondrial elements become so fine 

 that it is difficult to tell whether the yolk is being formed from 

 them or not. 



In preparations of frog ovary by the Mann-Kopsch method {18) 

 the mitochondria of the oocyte impregnate in a different manner 

 from the yolk, 'and no certain transitional forms between the 

 mitochondria and the yolk can be noted. We consider that the 

 matter is not settled. 



By the Mann-Kopsch method the full-grown frog oocyte cyto- 

 plasm is found to contain enormous numbers of granules which 

 fall into three categories, according to the manner in which they 

 act in the osmium tetroxide. There are, firstly, fine evenly sized 

 grains which go brownish to black ; these have been identified as 

 the mitochondria. There are, secondly, the very large yolk bodies, 

 which go yellowish ; then one finds intermediate forms which go 

 black in the osmium solution. These granules intermediate in 

 size may be derived from, and represent, the Golgi apparatus of 

 the frog oocyte. Sufficient work on this problem has not been 

 carried out to enable us to make quite certain as to the identity 

 and origin of the intermediate or black granules, and as to whether 

 the large yolk granules and the smaller mitochondria are in any 

 way related to the black granules. 



The granules, hitherto called *' yolk," are in the case of the 

 frog oocyte of at least three different kinds, whose histo-chemical 

 reactions are different in each case. 



About twelve years ago Lams (27) carried out some w^ork on 

 the formation of the " vitellus " of the amphibian egg. Lams 

 used no Golgi apparatus method, and he did not go very deeply 

 into the question as to whether the mitochondria metamorphose 

 into yolk. In the oogonium Lams finds an archoplasm contain- 

 ing a centrosome and surrounded by a halo of mitochondrial 

 substance. During growth the mitochondria multiply with the 

 archoplasm as their centre, so that the former become surrounded 

 by a thick mass of mitochondria. The archoplasm Lams calls the 

 yolk body (corps vitellin), and the mitochondrial cloud he calls 

 the yolk-forming mass (masse vitellogene), believing that the mito- 

 chondria of the frog are in some way connected with the formation 

 of the yolk. 



We have gone into the subject of the behaviour of the 

 mitochondria in the oogenesis of the Amphibia. What Lains 

 describes with regard to the evolution of the mitochondria is in 



