COMMON FROG. 101 
vations; but the comparatively low temperature of our 
spring, and the cold frosty nights which occur in March 
and April, may well account for such a discrepancy. If 
the eggs be deposited at the middle or latter end of March, 
it is generally, with us, the latter end of April before they 
are hatched. The situation of the mouth is now distinctly 
visible, though the opening is but small; and even when it 
becomes considerably enlarged it has no power of move- 
ment, and there are no distinct lips. The branchiz now 
speedily enlarge, and each of the two branches on either 
side is seen to consist of about four leaves (figs. 6. 9); 
these are sessile upon the body or stem of the branchia ; 
they are somewhat granular on the surface, and slightly 
irregular in their form; there is also frequently a short 
additional branch at the base of the posterior one, as is 
shewn in the outline, figure 9. The present state of these 
organs, which have now arrived at their maximum of de- 
velopment, constitutes one of the most charming objects for 
microscopic observation which can be conceived, and to 
view which a very high power is not necessary, nor even 
desirable. The current of the blood poured in regular 
pulsations at each contraction of the heart, passes up 
each stem or main branch of the branchie, and a dis- 
tinct stream is given off to each leaf; it is propelled to 
the extremity, and then returns down the opposite sides 
in the most regular manner, and the parts are so trans- 
parent that every globule of blood is distinctly and beauti- 
fully visible. 
This state of things, however, is destined to last but 
a short time. No sooner have these interesting organs 
attained their greatest developement than they begin to 
diminish in size ; they become obtuse (fig. 7), and are gradu- 
ally so reduced as to be withdrawn within the branchial 
