II HABITS AND NATURAL HISTORY OF THE FROG 45 



early in the season, frogs breed much earlier than in water 

 which on account of its depth or the lack of sunshine is 

 heated only very slowly. In masses of water fed by cool 

 springs the breeding of frogs and of other forms of life is 

 much delayed. 



The different species of frogs breed at different times. 

 In Germany Rana fusca breeds generally in March. In 

 Rami arvalis the association of the sexes commences two 

 or three weeks later, but the time of the egg laying nearly 

 coincides, according to Born, with that of the preceding 

 species, but its duration is somewhat longer. Rana esculenta 

 lays eggs only in May or June. 



The breeding period of a species naturally varies with the 

 latitude, coming on later as we pass northward and earlier 

 as we pass south. Thus Rana teniporaria, whose breeding 

 season in England and middle Europe is in March, does not 

 breed until May in Norway, but in southern countries it may 

 breed even as early as January. 



Dr. Morgan^ has recorded the results of four years' observa- 

 tions of several American species of frogs in the vicinity of 

 Baltimore, Maryland. 



"The first frogs to lay, and among the very first {Acris 

 gryllus excepted) to appear, are the wood frogs {Rana 

 sylvatica). A few warm days in early spring suffice to bring 

 them out. The following records give a general idea of the 

 time. February 23, 1891, and March 8th, 9th, and loth, 

 1880. The eggs of these had been laid several days. The 

 tgg bunches are found in small pools on the edges of weeds, 

 generally among the low hills, and are often stuck to twigs 

 of bushes. The bunches are generally large, four to six 

 inches in diameter, and contain very many good-sized eggs. 

 In the same pools it is quite usual to find the firmer egg 



1 Morgan, Am. Nat., Vol. 25. 



