^ 6 THE MICROSCOPE. 



marvel from beginning to end. I have sometimes 

 removed them quickly from the freezing apparatus, 

 and thrown them into a stove heated to 80 u Centig. 

 (176 Fahr.); when they emerged from this they 

 were seen to recover their animation, and run about 

 full of life. In this twofold test t and formidable 

 transition from cold to heat, these Microzoa passed 

 rapidly through a change of 120 Centig. (216 

 Fahr.) without being in the least inconvenienced by 

 it." After what I have said and quoted, I am sure 

 you will wish to make a few " slow-going" acquaint- 

 ances. 



CHAPTER VI. 



USE OF THE MICROSCOPE IN ZOOLOGY (continued}. 



ONE of the most interesting spectacles afforded by 

 the microscope is that which is furnished by the cir- 

 culation of the blood. This may readily be seen in 

 the gills of the tadpole or newt, in the tail of the tad- 

 pole, the foot and tongue of the frog, in newly-hatched 

 fish, such as young trout, perch, sticklebacks, &c. 

 The tadpole in its early stages of existence is essen- 

 tially a fish, breathing the air contained in the water 

 by means of external gills alone. If you will examine 

 a very young tadpole, you will see these gills in the 

 form of a pair of fringes at the sides of the head ; at 

 the bases of these are also the rudiments of the in- 

 ternal gills. The external gills rapidly disappear at 

 the end of four or five days; but the internal gills, 

 which were mere rudiments at first, are undergoing 

 rapid development. " It is requisite," says Dr. Car- 

 penter, " that the tadpole subjected to observation 



