158 WORLD-POWER AND EVOLUTION 



water, and there the egg-laying and fertilization took place. The 

 gelatinous envelopes of the eggs which usually remain unswoUen 

 and sticky on the land, swelled up and would not adhere to the 

 male's legs. Hence the young developed freely in the water with- 

 out the paternal care. After this had happened during several 

 of the breeding periods, of which two, three or four occur each 

 summer, the toads acquired the habit of going to the water, and 

 the eggs became more numerous and smaller. 



More important than this, however, is the fact that, according 

 to Kammerer, the offspring produced in this way showed a change 

 of habits like that of their parents. At* the time for reproduction 

 they sought the water, even when kept at the normal temperature, 

 and laid their eggs there. Moreover, in the fourth generation 

 there appeared on the forefinger of the male a swollen pad which 

 was absent in the race that Kammerer began experimenting with, 

 but which seems to have belonged to ancestral types. Thus a 

 change in climatic conditions seems to have caused a permanent 

 mutation. The mutation, to be sure, like some of those of the 

 butterflies, seems to have been back toward an ancestral form. 

 This, however, by no means indicates that mutations may not 

 take place in the opposite direction. Such seems to have been 

 the case with Hoge's drosophila where the change if carried far 

 enough might lead to a wholly new type of fly with an additional 

 pair of legs. 



By exposing the larvae of the nurse-toad to cold conditions, 

 Kammerer produced results of quite a different kind. He pro- 

 longed the larval condition even to the time of sexual maturity. 

 When the offspring of such forms were placed under normal 

 conditions of temperature the abnormal duration of immaturity 

 was found to be inherited. Here, as in the other cases, the in- 

 herited effects appear to be produced very early in the life of 

 the organism. The heat to which the toads were subjected 

 apparently influenced the eggs while they were still in the mother's 

 body, and the cold of the other experiment was effective at an 



