148 
ANIMAL PEDIGREES. 
July, 1891. 
ancestral history of frogs. At the time of hatching, Fig. 16, 
there are no limbs and no lungs; the heart, the alimentary 
canal, and the nervous system are in an extremely imperfect 
condition; while other organs of the adult frog, such as the 
kidneys, have not yet commenced to appear. The frog has, 
therefore, to effect the greater part of its development after 
the time of hatching. 
In the little West Indian frog, Hvlodes, Fig. 22, the 
course of events is very different. This frog, which is of small 
size—less than a couple of inches in length—lays its eggs 
not in water but on the leaves of plants. The eggs are large, 
having a diameter of about -J- inch, i.e ., are about three 
times the diameter and twenty-seven times the bulk of the 
eggs of the common English frog ; compare Figs. 15 and 19, 
which are drawn to the same scale. The large size of the egg is 
caused, as we have seen, by great abundance of food yolk; 
and the consequence of this large supply of food yolk in the 
egg of Hylodes is that the frog is enabled to complete the 
whole of its development before hatching, and emerges from 
the egg capsule, Fig. 21, in a form differing from the adult 
merely in the possession of a rudimentary stump of a tail; 
and even this disappears before the close of the first day of 
its existence, Fig. 22. 
A further and direct consequence of this development 
within the egg is that the successive stages are hurried over, 
and are at best but imperfectly recapitulated. Thus, although 
Hylodes passes through what may be called a tadpole stage, 
Fig. 19, yet it never develops gills ; so that were Hylodes 
the only frog known to us, it is very likely that we should 
have arrived at wrong conclusions concerning the pedigree 
of frogs. 
The influence of food yolk on the development of animals 
is closely analogous to that of capital in human undertakings. 
A new industry, for example that of pen-making, has often 
been started by a man working by hand and alone, making 
and selling his own wares; if he succeed in the struggle for 
existence, it soon becomes necessary for him to call in others 
to assist him, and to subdivide the work; hand labour is soon 
superseded by machines, involving further differentiation of 
labour; the earlier machines are replaced by more perfect 
and more costly ones; factories are built, agents engaged, 
•and, in the end, a whole army of workpeople employed. In later 
times a man commencing the same business with very limited 
means will start at the same level as the original founder, 
and will have to work his way upwards through much the 
same stages, i.e., will repeat the pedigree of the industry. 
