go6 a Sir Everard Home on the formation of fat 
more fat is deposited, but all that was previously formed is 
found to have been consumed, in producing the metamor- 
phosis into the frog : which leads me to conclude, that such 
a deposit of fat is necessary to the metamorphosis of a tad- 
pole into a frog, and that such unusual length of intestine, is 
required to admit of so large a quantity of fat being formed 
in so short a time, and, therefore, that the intestine is the 
laboratory in which the fat is formed. 
To ascertain, whether the necessity of such a supply of fat 
is occasioned by the soft parts of the tadpole not being con- 
vertible into bones, and other parts of the frog, which did not 
exist in the tadpole, or, simply, from a deficiency of materials, 
I have had the assistance of my friend and fellow labourer in 
animal chemistry, Mr. Hatchett, who some years ago ascer- 
tained, that the yelk of an egg is essentially composed of 
concrete oil, combined with a small proportion of albumen, 
and he has made out the following important facts. “ That 
the spawn of the frog, has no yelk, and contains no oil what- 
ever; he also corroborates Mr. Brande's statement, that it 
consists of a substance intermediate between albumen and 
gelatine, inclining principally to the former. That the ova 
of the shell snail, both of those that have a shell, and those 
that have only a strong membranous covering, have no yelks, 
and consist of albumen, since they coagulate in proof spirit of 
wine, and, when so coagulated, and examined some time 
afterwards, appear not to contain any oil. That the ova of 
the lobster have no yelk, and contain no oil. 
But he remarks, that the spawn of the lobster, when recent, 
is filled with albumen mingled with a substance of a dark olive 
colour, and whilst the former as usual is coagulated by heat. 
