RANINAE 



255 



Both sexes can croak, and this sound is frequently produced 

 under water ; but there are no regular concerts, although many 

 collect in the same pond or spring, which is perhaps the only 

 suitable place for miles around. The male puts its arms around 

 the chest of the female, behind her arms, and the embrace is so 

 firm that nothing will induce him to loosen his hold. The process 

 becomes an involuntary retlex-action, a cramp which may last for 

 days, or even for weeks, if sudden cold weather sets in, until 

 the female is ready to expel the eggs, an act which is quick and 

 soon over. The usual time of spawning in Middle Europe is the 

 month of March, earlier in warm, later in cold seasons ; in 

 southern countries, February or even January, but in Norway 

 not until May. Although the males of this species are not 

 more numerous than the females, and therefore should be able 

 to mate without much trouble, their ardour is so great that they 

 occasionally get hold not only of the wrong kind of frogs, but of 

 toads or even fishes, and, if taken off by force, they fasten on to any- 

 thing else, a log or on to your 

 own fingers. The eggs measure 

 2-3 mm. in diameter, are black 

 with a whitish spot on the lower 

 pole, number from 1000 to 2000, 

 and sink at first to the bottom. 

 Their gelatinous cover soon swells 

 to a large globe more than 10 

 cm. in width, and the whole 

 mass, as large as a man's head, 

 floats on the surface, often stained 

 with mud and other impurities. 

 During the cold weather which 

 often prevails in the spring, the 

 dark brown larvae are slow in 

 their development ; and provided 

 with rather large branched ex- 

 ternal gills and a well-developed 

 tail, they wriggle about in the 

 dissolving slime for three or four 



weeks. Fischer Sigwart^ has timed 



Fig. 49. — Rana temporaria. Eight suc- 

 cessive stages in the development 

 from tlie egg to the almost complete 

 Frog. X 1. 



and measured them as follows. — The eggs were laid on the 10th of 



1 Zool. Gart. 1885, p. 299. 



