138 The Microscope. 



CHAPTER XII. 



CIECULATION OP THE BLOOD. 



|HE little tadpole suspended in the water at 

 No. 13 now claims our attention. He is an 

 individual of far higher standing than the 

 animalcules, being a vertebrated animal, and is the 

 tadpole of Rana temporaries, the common frog which 

 I mention because young toads and newts are also 

 called tadpoles when in their aquatic state. 



The microscopic spectacle which it presented to 

 especial advantage on April 10th, and for some days 

 later, was the circulation of the blood in the branchise 

 or external gills, those four hand-like appendages 

 which may be seen, two on each side of its head. 



Plate VIII., fig. 5, represents a few of the capilla- 

 ries in the web of a frog's foot, under a very high 

 magnifying power. Each of these is filled by a 

 transparent fluid, in which are to b seen the " isolated 

 floating cells " known as the "blood-corpuscles." 

 These are of two kinds, the " red " and the " colour- 

 less." The red always present the form of flattened 

 discs, which are circular in man and in most of the 

 beasts, and oval in the birds, reptiles, and fishes. They 

 are hollow, and contain a coloured fluid. The colour- 



