60 THE NATURE STUDY COURSE. 



The Frog's Relations. — Mud-puppies are large batrachians, 

 whose red, bushy gills persist throughout life. Salamanders 

 and newts or efts are lizard-like in body and limb ; but they 

 have smooth, viscid and usually spotted skin. In the adult 

 state they live chiefly upon snails, slugs, insects and worms, 

 and are quite harmless to man. Tree-toads look like small 

 toads, but they can easily be distinguished by the discs or 

 suckers on their toes. It is by these discs that they cling so 

 well to perpendicular surfaces. They, and to a less extent the 

 common frog, change the color of their skin. The inner skin 

 contains numerous color-cells or spots, which by contraction 

 or expansion change the general color of the body. It is a 

 question whether these color changes can be controlled by the 

 animal ; probably they arise automatically under the influence 

 of the color of the environment through the eye upon the 

 sympathetic nerves and those of the skin. All these animals 

 have a tadpole stage, which differs from the higher fishes in 

 no other important way than in the absence of fin rays. This 

 stage is quite as interesting to the younger children as the 

 adult one. Intelligent observation of the segmentation of the 

 egg, the transformational steps, and the details of structure 

 is good exercise for the advanced classes. Choose from the 

 following outline the parts suited to the pupils whose observa- 

 tions you may be directing. 



The Eggs. — Search ditches and shallow ponds in early spring 

 for masses or strings of jelly containing small eggs resembling, 

 except for the black spot in each, so many 

 grains of swollen tapioca. Eggs embedded in 

 jelly found in the situations named will pro- 

 bably prove to be either those of the toad or 

 the frog. Should they turn out to be sala- 

 mander's or tree-toad's, they will be none the 

 less interesting. Frog's eggs are found in 

 jelly masses, toad's eggs in strings of jelly. 



