FEOG 263 



times. Make a slip noose in the ends of three 

 or four threads, tighten the nooses around the 

 tips of the toes, and by fastening the threads at 

 different points on the board, lightly spread the 

 web over the hole. Keep the frog under the 

 influence of chloroform, and keep its body moist 

 by spreading over it a damp cloth or a layer of 

 wet, absorbent cotton. Examine the web with 

 a low power, noting the pigment cells and the 

 blood-vessels. Put a drop of water on a part of 

 the web, lay on it a bit of cover-glass which 

 will fit between the toes, and examine the prep- 

 aration with a high power. Study the flow of 

 blood in the various vessels, and note the be- 

 havior of both red and colorless corpuscles. 



C. Development. 



In the early spring, when the ice is leaving the 

 ponds and streams, frogs' and toads' eggs may be 

 found in abundance as slimy masses fastened to 

 reeds and water-plants, or floating on the surface. 

 Each mass consists of a number of small, black, 

 berry-like bodies, each of which is embedded in 

 a gelatinous matrix. One of these masses should 

 be transferred to the laboratory, placed in a large 

 jar of water, which should frequently be changed, 

 and the eggs examined from day to day. The va- 

 rious stages of segmentation may be studied, and 

 the development of the tadpoles watched. As 

 soon as the latter appear, they must be provided 

 with a supply of water-plants to which they may 

 attach themselves. 



For comparison with the frog make a general 

 examination of a fish or a bird. 



