THE DEVELOPMENT OF THE FROG. 159 
or regions of the body. And thus, at the fifth day of the egg’s 
existence, the interesting phenomena is presented to us which 
indicates the formation of a nervous system in our future frog, 
conveying to us the broad features of structure on which all 
vertebrate or back-boned animals are formed. Man’s own struc- 
ture corresponds in its broad lines, in a most remarkable degree, 
with that of a frog. In this egg of the frog, then, we have a 
source of information full of interest to all who care to study 
it, and carry it to its legitimate end, when they will be able also to 
clear up a few points of their own existence. With the formation 
of this groove the walls of the body are thrown downwards, and 
the organs contained in them are developed. On the sixth day 
there is a radical change, the sand glass shape caused by the 
groove has given place to the distinctive outlines of a head and tail. 
On the seventh day these become more marked still, until on 
the eighth day we have no difficulty in recognising the elementary 
outlines of the tadpole. 
On the ninth day the progress of development is very marked. 
The head and tail, which were previously in a folded position on 
the body, begin to open out. About the end of the ninth day, if 
we observe carefully, we become convinced that the mysterious 
principle which we call life has developed itself in this animal, and 
that it is actually able to feebly wag its tail. 
You will have observed in this division of the ovum the 
interesting fact has become apparent that the embryo frog, unlike 
birds, &c., does not originate in a single vesicle or sac on the 
surface of the yolk, but that the whole substance of the yolk has 
become assimilated or transformed into the embryo tadpole. 
From this stage the observer cannot fail to be impressed with the 
fact that a rapid change is proceeding daily. The gills, the tail, 
and the nostrils develop somewhat quicky, while the little animal 
is also seen to be daily, or rather I should say hourly, gaining in 
strength and activity, until at the fourteenth day it is seen to put 
forth all its energy in bringing its head and tail together with a 
jerk. These desperate efforts are interesting and instructive, 
because it teaches us that it is exerted to free it from the cords 
which bind it to the centre of its transparent sphere. At the end 
of a series of desperate struggles the little animal seems quite 
exhausted, but it gradually moves forward till it finds its way to the 
outside of the egg. But, like two fond friends loath to part, it 
takes up its abode for the next two days on the outside of the 
egg, and thus absorbs all that remains of the nutritious fluid inside 
the egg, while it occasionally indulges in a vigorous wriggle. As 
it gains in strength it is seen to make short excursions, thus testing 
its power of swimming. ‘These excursions become more frequent, 
and are gradually extended in length, serving the double purpose 
