coo PROBLEMS OF GENETICS 



definite example, and because it is the case which most readily 

 admits of repetition and verification. 



The habits of Alytes obstetricans are well known. The 

 animals copulate on land. As the strings of eggs leave the 

 female they are entangled byjjhe hind legs of the male, and being 

 adhesive they stick to him ind undergo their development at- 

 tached to his back and legs. The number of eggs varies from 18 

 to 86, a number much smaller than is usual in toads and frogs 

 which lay their eggs in water. The eggs are large and full of yolk. 



There are two breeding seasons, one about April and the other 

 about September, and a winter hibernation. Not only animals 

 brought in from outside, but their offspring reared in domestica- 

 tion maintain these normal habits in confinement, if the temper- 

 ature does not exceed 17 C. (pp. 499 and 534). 



If, however, the temperature be artificially raised and kept 

 at 25-30 C, the males do not attach the eggs to themselves 

 when spawning occurs on land but let them lie. The adhesion 

 of the eggs is said to be hindered by the comparatively rapid 

 drying of their surfaces. 



More usually in the high temperatures the animals take to 

 the water and copulate there. The eggs are ejected into the 

 water, and as their gelatinous coverings immediately swell up, 

 they do not stick to the males. 



The offspring thus derived from the parents subjected to 

 heat for one breeding-period only, whether they were laid in water 

 or on land, did not show departures from the normal type. 



Kammerer states next, however, that in subsequent breeding- 

 periods the same parents frequently take to the water to breed, 

 though they have become quite accustomed to the heated 

 chamber; and furthermore that if such animals, having thus lost 

 their instinct to brood their young, be transferred to ordinary 

 temperatures they do not readily reassume their normal habits, 

 but for several breeding seasons — at least four — will take to 

 the water. These parents lay from 90 to 115 eggs, which are 

 small and contain little yolk, and the larvae, on hatching, breathe 

 with their embryonic gills until they are absorbed instead of 

 being broken off as normally. 



