100 RANADA. 
partly over the back ; and the head is distinguished from 
the body by a slight contraction at the neck; and a short 
period more suffices to bring it to the condition represented 
in figures 3, 4, of the woodcut, in which the branchiz are 
seen to consist of two tubercles on each side, as yet simple 
and undivided ; the holders, which are small simple organs 
placed near the situation of the future mouth, and which 
serve to enable the little animal to attach itself by means 
of a viscid secretion at their extremities, have become 
longer, the web, or fin, is also enlarged. By this time the 
first voluntary motion of the embryo is discovered on the 
application of any means of excitement or disturbance ; but 
it consists only of a slight movement of the head or tail. 
The nostrils are seen more distinctly, but the mouth is 
scarcely yet observable, and shortly afterwards the eye, in 
a rudimentary state, may be just discerned. The next step 
in the developement is a slight division of the branchiz into 
lobes, and the appearance of that beautiful and interesting 
phenomenon, the circulation of the blood through these 
organs. The embryo, which is still confined to a curved 
position by the envelopes (fig. 1), is now seen frequently to 
extend itself by sudden jerks, as if to emancipate itself 
from its confinement, which it eventually does by tearing 
the membrane of the egg. The Tadpoles, we see, are now 
hatched (fig. 5). According to Rusconi, this takes. place 
within four days after the deposit of the eggs, in a tempe- 
rature varying only from 23° to 27° Centigr. (73°:4 to 
80°°6 Fahr.) ; but certainly in our own climate, in the 
ordinary temperature of our spring, it does not take place 
until at least a month. As I before observed, the develope- 
ment may be greatly hastened by a constant elevation of 
temperature, and I was often surprised at the degree to 
which this was the case in the course of my own obser- 
