ADAPTATION 201 



The offspring thus abnormally developed when they mature 

 are said never to brood their eggs. If they are derived from 

 the earlier spawnings of their parents, before, that is to say, the 

 parents had been submitted to the changed conditions long enough 

 to transmit their effects, they lay on land ; but if they are derived 

 from the later spawnings, they lay in the water. These changes 

 of habit are manifested without the continued application of 

 the abnormal experimental conditions, and, as I understand the 

 account, in normal conditions of temperature. 



If the abnormal experimental conditions are continued, the 

 toads always lay in water, and their eggs become progressively 

 smaller and more numerous. The larvae in the fourth generation 

 acquire three pairs of gills instead of one pair, and are in other 

 respects also different from the normal form. 



Respecting the Alytes bred in this way Kammerer makes the 

 very striking statement that the males in the third generation 

 (p- 535) h ave roughened swellings on their thumbs and that in the 

 fourth generation (pp. 516 and 535) these swellings develop black 

 pigment. Together with the appearance of this secondary sexual 

 character there is hypertrophy of the muscles of the fore-arm. 

 To my mind this is the critical observation. If it can be sub- 

 stantiated it would go far towards proving Kammerer's case. 

 Alytes, among toads and frogs, is peculiar in that the males do 

 not develop these lumps in the breeding season, and the fact 

 may no doubt be taken to be correlated with the breeding habits, 

 copulation occurring on land and not in water as is usual with 

 Batrachians. It is to be expressly noticed that these lumps on 

 the thumbs or arms of male toads and frogs are not merely pig- 

 mented swellings, but are pads bearing numerous minute horny 

 black spines, which are used in holding the females in the water. 

 The figures which Kammerer gives (Taf. XVI, figs. 26 and 260) 

 are quite inadequate, and as they merely indicate a dark patch 

 on the thumbs it is not possible to form any opinion as to the 

 nature of the structure they represent. 



The systematists who have made a special sudy of Batrachia 

 appear to be agreed that Alytes in nature does not have these 

 structures; and when individuals possessing them can be pro- 



