‘T'HE MICROSCOPE. 103 
Leaving out the question of origin there is, from numerous recorded 
observations, no doubt that the above is the method of development 
of the fat cell in the higher vertebrata. In my observations on the 
method of development of the fat cell of the frog, on the contrary, I 
have never seen the fat first appear in the above described manner. 
The fat is deposited in a single drop only, and the first appearance 
of fat in the cell is synchronous with nuclear division. 
Activity of the cell nucleus has never been described, so far as I 
am aware as part of the process of cell development in the fat cell, 
the nucleus being only spoken of as passively displaced and crowded 
to the side of the cell by the accumulating fat. 
In contrast with this, my observations on the development of the 
fat cell of the frog show that, next to the formation of fat, activity 
of the cell nucleus is the most striking feature in the process, and 
that the change undergone by the nucleus during the development 
of the cell is both important and interesting. 
As the first step in development, the nucleus of the special 
plasma cell widens laterally and the intra-nuclear reticulum separates 
into two, forming an intra-nuclear line, along which the nucleus 
afterward divides. (Fig. 1. AA.) 
Immediately after the formation of the intra-nuclear line, and 
while the nucleus not yet separated into two, has the appearance of 
two nuclei in close apposition, a minute droplet of fat is formed and 
deposited in the cell body at one end of the line. This accumulation 
of fat grows in size, and the nucleus divides along the intranuclear 
line, the division beginning at the end of the line next the fat. The 
fat follows into the space so formed like a wedge, separating the two 
portions of the nucleus. (Fig. 1, B.C. Fig. 3, F.) This process 
continues and completes the division of the nucleus. (Fig. 1, D. D.) 
As the cell still continues to form and deposit fat in its interior, the 
separated nuclei are pushed further and further apart, and become 
more flattened in shape, as if by pressure from the accumulating fat, 
the intra-nuclear reticulum progressively becoming more and more 
indistinct. (Fig. 1, F. H.) 
The fully matured fat cell has the usual form of the fat cell, a 
very thin protoplasmic covering, enclosing a large drop of fat. 
There are, however, two flattened and peripherically placed nuclei 
instead of one. It is difficult, however, in examining sections of a 
fat body taken in the summer from a well nourished frog, when all 
the cells are developed, to satisfactorily demonstrate that each cell 
has two nuclei, the cells being so fully distended with contained fat, 
and so crowded together as to make the exact relation of each 
