VERTEBRATE ZOOLOGY. 475 



of Johns-Hopkins University, on the differences manifested 

 in the larvae of Ainbly 'stoma. This genus is especially inter- 

 esting by reason of the great variation as to the time of cast- 

 ing the gills, and the assumption of the adult characters in 

 the different species, long ago pointed out by Cope ; and also 

 because in one species of the genus, found in Mexico the 

 famous Axolotl the animal seems to be normally arrested, 

 in its native place, in its development, and rarely, if ever, to 

 pass beyond the larval stage. The observations of Mr. 

 Clarke relate to the individuals of one and the same brood; 

 the species was supposed to be Amblystoma opacum. In 

 the early part of spring the eggs are laid in masses of from 

 5 to 200, attached to water plants or overhanging blades of 

 grass. Some of these, being transferred to glass jars, were 

 found to rapidly develop, and the rate of growth seemed to 

 be largely determined by the purity as well as temperature 

 of the water. Nevertheless, there were, almost from the first, 

 considerable individual differences, and "among the many 

 there were a few who, although they came from the same 

 parents, and were subjected to the same conditions while in 

 the egg, were yet gifted with greater vigor and energy than 

 most of their brothers and sisters or cousins." These vigor- 

 ous fellows nibbled at the gills of their weaker kindred, and 

 the consequence was that the growth of the latter was re- 

 tarded by the diminished aeration of the blood caused there- 

 by, and the reduced power to obtain food supply, while the 

 former flourished in inverse ratio. The discrepancy between 

 the two thus rapidly increased ; and " within a week or ten 

 days from the escape from the egg, these favored few were 

 fifty per cent, larger than their weaker comrades who were 

 born upon the same day." Their mouths had then become 

 sufficiently large to enable them to ingest some of the weak- 

 er ones, and this they did not hesitate to do. "This great 

 increase in the supply of food soon produced a marked effect 

 upon those who were thus supplied, so that in ten days from 

 the time that they began to feed in this way they were from 

 ten to twelve times the length and bulk of those upon whom 

 they were feeding." All the weaker individuals were thus 

 eliminated, and actually aided " the stronger ones by serving 

 them as food until they could pass through their changes and 

 escape to other regions where food was more abundant." 



