THE TADPOLE. 



If possible the pupils should have a chance to examine 

 tadpoles of different ages. These can readily be obtained by 

 collecting the eggs in the spring and allowing them to hatch 

 out in glass jars. A number of these can be killed at various 

 stages by means of picrosulphuric acid (see Introduction) used 

 for a couple of hours, then washed two to three hours in water, 

 and preserved in 70% alcohol. The earliest stage necessary 

 should show the external gills; the latest, which are more 

 easily obtained from the ponds, should have the hind legs well 

 formed. 



In the earliest of these larvae the pupil should pay 

 especial attention to the gills. How many are there? 

 Are they fringed? How do they differ from the gills of 

 fishes? What is the relative size of head, bodv and tail? 



/ 



In the older larvae the jaws should be examined. What 

 is their nature? What is the size of the mouth compared 

 with that cf the adult? On the left side of the body see 

 the opening of gill-chamber. Is there one on the right 

 side? Carefully open this chamber, taking great pains not 

 to cut too deeply. Do the right and left sides of the gill- 

 cavity connect? Can you find any traces of the fore 

 limb? Carefully open the abdomen and notice the com- 

 pact coiling of the intestine. Is it relatively longer or 

 shorter than in the adult?" Examine the tail with its fin. 



Is there a skeleton to the fin? Is the tail homocercal or 



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