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 branchiae 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 branchiae, 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 ally so reduced as to be withdrawn within the branchial 



