The Role of the Chromosomes 223 



observation on the change induced by transferring the rab- 

 bits from Porto Santo to England. 



Great differences also have been produced in butterflies 

 and moths by changes in the food of the caterpillar, while 

 light, electric and chemical stimuli, etc., show marked effects. 



The results of some American workers will now be con- 

 sidered in more detail. 



The salamander Amblystoma has gills and fins and lives 

 in the water during its larval or axolotl stage. At metamor- 

 phosis it loses fins and gills, leaves the water and thereafter 

 lives upon the land. In some cases however metamorphosis 

 does not occur, and sexual maturity appears in the larval 

 form. Although the relationship between the axolotl and 

 some terrestrial form was suspected by Cuvier, it was not 

 discovered until 1865 in the Jardin des Plantes at Paris, 

 when the young of some axolotls gradually lost their gills, 

 their fins disappeared and they came forth upon land to live 

 thenceforward as Amblystomas. All the factors controlling 

 the metamorphosis cannot at present be stated with certainty, 

 but apparently a regular but small supply of food as opposed 

 to abundant but irregular feeding tends to prevent meta- 

 morphosis. It has been generally supposed that drying up 

 of the water, with consequent lack of oxygen, forced the sala- 

 manders to an air-breathing habit and induced metamorphosis. 

 But Powers has shown that the axolotl will metamorphose in 

 abundant and well-aerated water, if its food supply be cut 

 off, and conversely forcing the salamanders out of the water 

 will not induce metamorphosis unless accompanied by a 

 change from an abundant to a meagre diet. His explanation 

 of the control of metamorphosis by nutrition is that, when 

 suddenly deprived of food, the salamanders are forced to 

 live on their own tissues, and that those of gills and fins 

 being the first consumed, causes the reduction of these organs, 

 and induces metamorphosis. His interpretation is supported 

 by the fact that during metamorphosis the animals are gener- 

 ally in a state of semi-starvation. 



As is well known, Amblystoma is an exceedingly variable 

 animal, and Powers has related these variations in large 

 measure to nutrition. Regular, but moderate amounts of 

 food, produces slender and agile animals, while heavy feeding, 

 on the contrary, produces fat and lazy beasts, which spend 

 most of their time on the bottom of ponds or aquaria. Most 

 marked of all the varieties are certain animals of large size, 

 very broad heads and frequently emaciated appearance, 

 which result from cannibalism. Axolotls ordinarily feed 

 upon microscopic life in the water such as larvae of insects, 



