
528 THE AMERICAN NATURALIST. [Vor. XXXVI. 
nuclei appear red, the yolk blue, and the cell outlines are 
brought out with great clearness. 
THE FORMATION OF THE BLASTOPORE. 
The egg of Bufo lentiginosus probably contains a greater 
amount of pigment in proportion to its size than that of any 
other common amphibian. It is, therefore, very difficult to 
study the movements of individual cells before and during the 
formation of the blastopore, as has been done to some extent in 
the eggs of several other species of amphibians, where the pigmen- 
tation is less extensive and cell outlines can be readily determined. 
In the egg of Bufo the pigmentation extends in all cases 
some distance below the equator, and I have frequently found 
eggs in which fully three-fourths of the surface was deeply 
pigmented before the appearance of the blastopore. Indi- 
vidual eggs, even from the same female, differ greatly in the 
amount of pigment they contain. Asa rule, the pigment line 
extends farther down on one side of the egg than on the other, 
as seen in Fig. 1, agreeing in this respect with the frog’s 
egg according to Schultze (24), Morgan and Tsuda (17), and 
Wilson (27). 
Sections through an egg at the close of the blastula stage 
show a large segmentation cavity in the upper hemisphere. 
Its dorsal wall is formed, as in the frog, of three or four layers 
of small angular cells of uniform size. The cells forming the 
outer surface of the egg are almost completely filled with 
pigment granules, and a considerable amount of pigment is 
scattered throughout all the cells of the upper part of the egg. 
The yolk cells below the segmentation cavity are much larger, 
more rounded, and stain less intensely than the cells in the 
upper hemisphere. There is the same gradual increase in the 
size of the cells from the upper to the lower pole that other 
investigators have noted in the frog's egg. 
The dorsal lip of the blastopore invariably appears some dis- 
tance below the equator of the egg, but never in the middle 
of the lower hemisphere, as maintained by Houssay (8) for the 
axolotl and Jordan (9) for the newt. 

