THE AMERICAN NATURALIST [Vol. XLIII 



Chambers experimented with eggs of Rana temporaria and B. 

 esculenta, and his object was to determine how the initial size 

 of the eggs and temperature affect the size of developing embryos. 

 He found that the eggs of both species show considerable varia- 

 tions in size, that are in no way connected with the prevailing 

 temperature of the locality from which those eggs are collected. 

 The average size of eggs varies not only with the species or 

 locality, but also with each individual frog. Furthermore, eggs 

 laid by one frog also present variations in size, which, in one 

 case, were 1.8 mm., 1.2 mm., 1.15 mm., and 1.05 mm. in diameter. 

 The eggs measuring 1.15-1.20 mm. were most abundant. 



Contrary to what one might expect, there is no relation be- 

 tween the size of frogs and the size of eggs which they lay, and 

 small frogs with large eggs as well as large frogs with small eggs 

 are frequently found. 



In the first place Chambers undertook to determine the rela- 

 tion of the size of an egg to the rate of its development and sub- 

 sequent growth of the embryo. He divided eggs of a single frog 

 into lots according to their sizes, and found, on rearing those, 

 that small eggs have a tendency to develop slightly faster than 

 large eggs. This tendency is marked only in the early stages, 

 for as the tadpoles commence to feed those developing from large 

 eggs grow faster and pass through metamorphosis sooner. 2 On 

 rearing eggs of two lots, one containing eggs of large and uni- 

 form size, the other containing eggs of various sizes, it was found 

 that the size of tadpoles varied considerably in favor of the 

 former. Besides, the tadpoles of the first lot have all meta- 

 morphosed in course of two weeks, while two months have elapsed 

 before the tadpoles of the second lot had all metamorphosed. 

 There is one point in connection with this experiment on which 

 unfortunately Chambers gives no information, and yet it may 

 alter the conclusion drawn from the experiment. He mentions 

 that there were 70 eggs in the first lot and 100 eggs in the 

 second lot. If the eggs of both lots were distributed in an equal 

 number of dishes there must have been fewer eggs of the large 

 size than of the mixed sizes to each dish. The difference in the 

 rate of development and in the size of tadpoles might have been 

 therefore caused by the more or less crowded condition of the 

 eggs, and not by the large or small initial size of the eggs. In 

 fact, Chambers resorts to this factor of the number of eggs de- 

 2 See page 7. 



