i8 THE PHYSIOLOGY OF REPRODUCTION 



condition he regards as comparable to that which occurs during the 

 " heat " period of a mammal. 



Amphibia 



The intimate connection between sexual periodicity and climatic 

 variation exhibited by many Amphibia and Eeptilia, especially in 

 temperate climates, was commented on by Spallanzani.^ This close 

 dependence upon environmental conditions is evidently due largely 

 to the habits of life of these animals, many of which hibernate or 

 show great sluggishness in cold weather ; while among Amphibia it 

 must be associated with the further fact that, whereas most members 

 of the group live to a great extent upon land, it is necessary for 

 them to deposit their eggs in water. Spallanzani concludes that 

 the reason why Amphibia are subject to a variation which is not 

 observable in birds and Mammals is because the former, like insects, 

 are cold-blooded, and have a comparatively small supply of internal 

 heat to animate them when it is cold. " As therefore the exercise 

 of their functions depends on the heat of the atmosphere, their 

 amours will also depend upon this cause, and will, of course, be 

 later in cold than in hot climates, and in both will vary with the 

 season." 



Spallanzani illustrates the truth of this fact by pointing out that 

 various species of frogs and toads begin to propagate earlier in Italy 

 than in Germany or Switzerland.^ On the other hand he records 

 the observation that the tree-frog and the fetid terrestrial toad were 

 populating in the ponds and reservoirs of Geneva in March, at a 

 time when in Lombardy they had not yet quitted their subterranean 

 p,bodes. 



It is interesting to note that in the frog and other Amphibia 

 the ova are produced in winter, when the animals eat little or nothing, 

 just as the genital organs of the salmon develop during the period 

 of migration, when the fish have practically ceased to feed. 



Bles ^ has discussed at some length the conditions under which 

 it is possible to induce various species of Amphibia to breed in 

 captivity. He states that the most necessary condition is that the 

 animals should be allowed to hibernate at the proper season, and in 

 order to accomplish this they must be in thoroughly good health 



1 Spallanzani, Dissertations, vol. ii., London, 1784. 



2 In the common frog [Rana temporaria) the usual time for spawning in 

 Middle Europe is March, earlier in warm, later in cold seasons ; in southern 

 countries, January or February, 'but in Norway not until May. Vide G&do-w, 

 Camh. Nat. Hist., vol. viii., London, 1901. This book contains a quantity of 

 valuable information concerning the breeding habits of many Amphibia and 

 reptiles. 



^ Bles, " The Life-History of Xenopus Icevis," Trans. Roy. Soc. Edin., vol. xli., 

 1905. 



