No. 2] THE OOGENESIS OF BUFO LENTIGINOSUS. 431 
over into yolk spherules. It is very probable that the aggre- 
gations of small yolk spherules shown in Figs. 55-56 have 
had such an origin, although it is possible that they were de- 
rived from the substance of a yolk-nucleus. During the early 
stages of yolk formation the cytoplasm at the outer boundary 
of the egg frequently appears vacuolated. This does not seem 
to be a constant phenomenon, however, and it may be due 
in part, at least, to the action of reagents. 
In the egg of Bufo there are two generations of yolk- 
nuclei, both formed from or under the influence of the vitelline 
bodies, and both evidently concerned in the formation of yolk. 
The first yolk-nuclei that are formed appear simultaneously 
in different regions of the cytoplasm and they later move close 
to the germinal vesicle where they gradually fade away. One 
can readily trace every step in their development from the stage 
of that shown in Fig. 46 to that of Fig. 56. The yolk-nuclei 
belonging to the second generation are formed at the periphery 
of the egg and they are transformed directly into yolk spher- 
ules. The various stages in the development of these bodies 
can also easily be followed. With these facts in mind the 
following statement by Crampton (24) is of interest: “The 
accounts of the origin of the yolk-spheres from cytoplasmic 
elements at places removed from the nucleus, or from several 
centres, or in all parts of the egg at once, fail to take into 
consideration an earlier stage marked by the origin from the 
nucleus of a true yolk-matrix which subsequently disintegrates 
and spreads throughout the whole cell-body as in Molgula.” 
It would seem as if enough cytological work had been done 
to make it clear that one cannot deduce general rules applica- 
ble to all eggs from the study of one particular egg, no mat- 
ter how carefully the work may have been done. 
According to my investigations the formation of the yolk 
in the egg of Bufo is closely associated with the vitelline bodies 
and also with the granular masses produced by them, the yolk- 
nuclei. I have elsewhere stated that the vitelline bodies are 
probably secretion products of the cytoplasm formed, possibly, 
under the influence of an enzyme given off by the nucleus. The 
