DEVELOPMENT OF FAT-BODIES IN EANA TEMPORARIA. 137 
This occurs at about the time that the mesonephric tubules 
are growing out towards the genital organ, forming the future 
vasa efferentia in the case of the male. Thus in some sections 
the condition of this double outgrowth from the excretory to 
the genital organs can be seen, the three parts of the nephros, 
pro-, meso-, and meta- being quite continuous. 
Ultimately the attachment of the fat-body to the kidney 
gives way, and the former remains attached to the anterior end 
of the genital organ, as it is in the adult (figs. 8 and 9). We 
thus see that the fat-body is not the anterior end of the genital 
organ, which has undergone fatty degeneration, as was thought 
by von Wittich, but that its attachment to the genital organ 
is secondary. 
The fatty degeneration is always complete before the attach- 
ment to the genital organ takes place ; almost any tailed Frog 
that has not very long had its four limbs showing the fat-body 
attached to the anterior end of the kidney. That it is, in 
reality, fat-body is shown by its macroscopic and microscopic 
characters, and by its staining with osmic acid. The part 
marked (/.) in fig. 7 has exactly the same structure and 
appearance as that similarly marked in fig. 8, the two specimens 
having been stained and cut at the same time. 
Having thus decided that the fat-bodies are derived not from 
the genital organs but from excretory structures, we have to 
consider what part of the nephros it is to which they owe their 
origin. It can only be pro-, meso-, or meta-nephros, or their 
ducts; the ducts can be at once put aside, because their 
destination has been clearly and definitely made out. The 
meso- and meta-nephros are also known to form together the 
permanent kidney, as found in the adult. 
There remains, therefore, only the pronephros, which, in the 
Amphibians at least, has hitherto received but little attention, 
though Sedgwick 1 mentions that it undergoes atrophy in the 
young Frog. “ Atrophy,” however, implies diminution in size, 
or even total disappearance ; the pronephros of the tadpole, 
on the contrary, not only persists but actually gets larger (in 
1 Op. cit., p. 445. 
