THE MICRUSCOPE. 101 
He is somewhat difficult to find, this little Demodex, owing to 
his great transparency, and a very careful search will often be neces- 
sary to discover him. 
I purpose, at some future meeting of this society, presenting 
some slides of this ectozoon as seen in various animals, with a more 
detailed description of the structure and organization of the parasite, 
of which it may truthfully be said to two-thirds of mankind: “ Like 
the poor, ‘ye have them always with you.’ ” 
PirrspureH, Pa. 
THE ORIGIN AND DEVELOPMENT OF THE FAT CELL 
OF THE FROG. (RANA HALECINA.) 
W. C. BORDEN, M. D., U. S. ARMY. 
[PLATE v. | 
N VIEW of the diversity of opinion which obtains in regard to 
the origin of the fat cell, it has seemed to me that a record of 
observations made by myself upon the origin and mode of develop- 
ment of the fat cell of the common marsh or leopard frog (Rana 
halecina), would be of interest. In certain of the lower vertebrata, 
of which the frog is one, the adipose tissue, instead of being scatter- 
ed through the body without regard to particular place, is found in 
certain definite localities only: being there accumulated into what 
are known as fat bodies, or corpora adiposa. The corpora adiposa 
of the marsh frog are two in number, and are situated at the dorsal 
side of the abdominal cavity in close relation with the kidneys and 
testes in the male, and the ovaries in the female. 
They are attached to the generative organs by bands of connec- 
tive tissue, and like them receive their arterial supply through sey- 
eral small branches of the dorsal aorta. Their veins are branches 
of the inferior vena cava. Each fat body consists of a main portion 
and several processes; and might be compared in form to the human 
hand, with its fingers increased in number and greatly elongated. 
They vary greatly in size in different individuals, and in the same 
individual at different seasons of the year. During the summer they 
are large and fully developed, nearly every cell being distended with 
fat. 
A microscopical examination made at this time gives only the 
usual appearance of fully formed fat tissue. In the early spring, how- 
ever, the fat bodies are smaller and most of the cells are undergoing 
development, and it is at this season of the year, that on micro- 
scopical examination will be found all the phases of development, 
from the undifferentiated cell, to the fully-formed fat cell, with its 
