DEVELOPMENT OF FAT-BODTES IN RANA TEMPORARIA. 139 
this — that with the close of larval life the pronephros is no 
longer needed, and in harmony with the pathological law that 
atrophy follows disuse, it degenerates to the condition of fat- 
body. Doubtless, however, this law is here so far modified 
that the fat-body still serves some useful purpose in the organism, 
though what that purpose is is not at all clear. It is in all 
probability an example of “ change of function,” the later 
function being in some way nutritive. 
As to the distribution of fat-bodies — they are unknown out- 
side the Amphibian group. According to Stannius, Hoffmann, 
Wiedersheim, and others, they are present in all Amphibians. 
We have very little knowledge of their function beyond that 
they are concerned in all probability with nutrition, serving 
as a reserve stock at certain times of the year. They are 
differently placed in the several groups in which they occur, 
and it is by no means certain whether they are homologous 
structures in all cases. 
The fate of the pronephros in the Frog, as above-described, 
throws some light on the condition that obtains in other 
groups of Vertebrates. 
It was stated by Balfour 1 that “ the pronephros atrophies 
more or less completely in most types, though it probably 
persists for life in the Teleostei and Ganoids.” 
In a later paper , 2 however, after working over the condition 
of the kidneys in the sturgeon and in certain Teleostei, he 
stated that “ the whole of the apparent kidney in front of the 
ureter, including the whole of the so-called head-kidney, is 
simply a great mass of lymphatic tissue, and does not contain 
a single uriniferous tubule or Malpighian body,” from which 
he concluded that both in Ganoids and in Teleostei the organ 
usually held to be pronephros is actually nothing of the kind. 
He therefore considered that Rosenberg 3 was mistaken in 
1 * Comparative Embryology,’ vol. ii, p. 729. 
5 “On the Nature of the Organ in Adult Teleosteans and Ganoids, which 
is usually regarded as the Pronephros or Head Kidney,” ‘ Quart. Journ. Micr. 
Sci.,’ vol. xxii, N. S., 1882. 
3 ‘ Untersuchungen iiber die Entwicklung der Teleostierniere,’ Dorpat, 
1867. 
