FROGS AND TOADS. 



87 



Note e.g. the rapid swelling of the jelly around the egg. 

 If got quite early pupils should be asked at once to examine 

 and draw the eggs, noting 



1. The dark end, the animal pole or living end. 



2. The white end the yolk substance which is to be used 



in the building of the tadpole's body. 



3. The jelly, which keeps the eggs apart, preventing 



collisions perhaps when the rough March winds 

 ruffle the pool, which certainly saves the eggs 

 from being eaten by all birds, save broad-billed 

 ones, and which may have other uses (Figs. 16 

 and 17). 



The following stages should be watched for and dates of 

 their appearance noted. A record should also be kept for 

 comparative purposes in successive years 

 of the external conditions as regards ex- 

 posure, light, temperature, and food sup- 

 plied. A strict account of the mortality 

 might be attempted so as to arrive at some 

 notion of the proportion reaching the frog 

 stage : 



Stage I. The mouthless stage. This is 

 first definitelv marked when the head 



Fig. 18. Tadpole 

 with external 

 gills. 



Fig. 19. Tadpole with internal gills. 



and body can be made out clearly. Note that now, 

 just as in the egg stage, breathing goes on through 

 the skin. 



Stage II. Appearance of external gills (Fig. 18). 



