WHITE AND YELLOW YOLK OF OVA ATT 
tive analyses, these spherules abound in fat. Of similar interest 
is the discovery of Miescher (’97) that at the time of the develop- 
ment of the eggs of the salmon the blood of these animals is unusu- 
ally rich in lecithin, fat and globulins. 
3. These two factors and the histological data 
One hardly has a right to mention the words ‘histology of yolk’ 
without entering upon the consideration of an enormous litera- 
ture. Since my own contribution is not primarily of histological 
nature, and for reasons stated at the outset, I refrain from doing 
so, although by my results I am seeking to put some rather new 
and additional interpretations upon histological conclusions, and 
to answer some questions in which histological, and to a less extent 
microchemical methods have before been largely used. 
The view that intermediate forms of spherules exist, connecting 
white yolk with the yellow yolk spheres, has been maintained by 
Rickert, Sarasin, Disse, Kolliker and others. The region under 
the germinal dise of avian, reptilian and selachian ova have fur- 
nished the most and the clearest pictures of the transition forms. 
Previous authors have, however, generally considered only the 
formation of the yellow from the white spheres during growth, 
and have not considered the reverse of this process as it occurs 
during the destruction of the yolk. Theengulfing of whole granules 
of (white) yolk by the entodermal cells has been recorded by His 
(00) and others. This I would observe is, if true, not a real con- 
tradiction of my thesis, since these granules doubtless later un- 
dergo the ordinary processes of digestion in the entodermal cell. 
Similarly I would note that the presence of yolk granules in 
follicular cells—demonstrated by many observers—only illus- 
trates the mechanism we have described at work in another cell; 
the classic example of this sort of formation being the fat globule 
in the cell of the intestinal mucosa. On the other hand the finding 
of such granules in a follicular cell is no guarantee whatever 
that the granule is thrown as such from that cell into the egg. 
The granule may here, as in the mucosa cell, again undergo diges- 
tion and pass from it in solution. 
