244 CHAPTERS ON EVOLUTION. 



the former species, which occurs 7.000 feet above the sea-level in 

 Wyoming territory, becomes transformed into the Amblystoma 

 Mavortium ; whilst the first Amblystomas obtained by Dumeril from 

 the Parisian Axolotls appeared to agree with another species of 

 Amblystoma (A. tigrinum). If these details be taken into account, 

 whilst they do not in the least affect the curious nature of the trans- 

 formation, they would seem to indicate that more than one species 

 of Axolotl undergoes metamorphosis ; and this result is exactly that 

 which the naturalist would be led to expect. The general condition 

 probably affects the whole Axolotl race, and is not confined to any 

 one species. Regarding the Amblystomas themselves, it has been 

 already remarked that these newts are well known in America. Over 

 twenty species are known to inhabit North America, and there can 

 be no doubt that these animals live and breed as true Amblystomas. 

 As Weismann remarks : " There are, therefore, true species of Siredon 

 which regularly assume the Amblystoma-form under their natural con- 

 ditions of life (i.e., develop into Amblystomas from eggs laid by 

 Amblystoma- parents), and which propagate in this form ; while, on 

 the other hand, there are at least two species which, under their 

 existing natural conditions of life, always propagate as Siredon " (i.e., 

 develop Axolotls from eggs laid by Axolotls). Observations by 

 Professor Baird on the development of Amblystomas show that, as 

 might be expected, the young gilled larvae, arising from Amblystoma 

 eggs, present a close likeness to the Axolotl race. 



The case of the axolotl illustrates powerfully the effects of a 

 change of surroundings in metamorphosing a species. A succession 

 of dry seasons, operating in the past, has most likely been the active 

 origin of the amblystoma race from the axolotl stock. Presumably 

 the axolotl, as the " gill-bearing " form, is the primitive stock ; the 

 amblystomas being a derived race, but nevertheless representing a 

 true species of which the axolotl, conversely, may be termed the 

 " larval form." To this relationship, however, reference will be sub- 

 sequently made. The shrivelling of the gills seen in the experiments 

 on the axolotl, it is noteworthy, was probably due to a mechanical 

 cause, that of dryness of the surroundings. Once established, the 

 new race of Amblystomas would be propagated amidst the conditions 

 which best suited them, whilst the axolotls have flourished amid 

 their own aquatic environments. 



This case of modification of species, however, leads to a much 

 more typical one in which the female of the black salamander of 

 the Alps, a gill-less newt or eft, retains her eggs within her body, 

 and hatches them ; the young likewise undergoing development, 

 and casting their gills therein, just as do the young of the modified 

 frogs already described. Furthermore, out of some 40 or 60 eggs, 

 only two young are developed ; the latter devouring the remaining 



