METHODS OF EXAMINATION 367 



gills, newly hatched tadpole, tadpole several days after hatching. 

 (Optional, a series of tadpoles showing metamorphosis.) x 15 to 20. 

 (Keep a record of the time day, hour, minute when each stage 

 was drawn.) 



EXPERIMENTS 



1. Keep some of the same spawn in a refrigerator for ten days, 

 then draw and compare with the eggs kept at normal temperatures 

 for the same length of time. 



2. At the time of formation of neural folds, free an embryo from 

 the albumen, and add carmine grains to the (shallow) water. Note 

 the direction of currents and motion of cilia. 



3. Amputate the tail of a newly hatched larva and observe the 

 result after a week or two. 



4. Find the (approximate) specific gravity of a tadpole by placing 

 one or two in each of the following solutions of gum arabic in water : 



Per cent by weight, 33 16.5 11 8.2 3.3 1.65 



Specific gravity, 1.11+ 1.06 1.037 1.028 1.011 1.006 



The solution in which they tend, when motionless, neither to rise 

 nor fall is of their specific gravity. Repeat with tadpoles just hatched 

 and with those one week, two weeks, three weeks, and four weeks 

 old. 1 



TOPICS FOR FURTHER STUDY 



1. Effect of heat and light upon development. 2. Capacity of 

 organisms for healing and regeneration. 3. Postembryonic develop- 

 ment of the frog, Arnblystoma, and Necturus. 4. General laws of 

 development. 5. Development of the chick. (This should be 

 illustrated by opening several eggs at various stages of development.) 



It may interest teachers to have reproduced here the examination 

 requirements of two universities which are exactly covered by the 

 preceding outline : 



1 See S. R. Williams in the American Naturalist, February, 1900, p. 98. 



