454 BULLETIN 34, UNITED STATES NATIONAL MUSEUM. 



They are very fond of raw meat, and, upon tlie slightest provocation, 

 they will feed upon each other. So I have found during the course of 

 my experiments that — 



"(7) The metamorphosis is hastened by regularly supplying the an- 

 imals with plenty of proper food. And what is still more interesting, 

 wlien they are thus treated it markedly affects the appearance of the 

 transformed Ambly stomas. 



"(8) If, during the process of forcing the transformation of Axolotls, 

 the animals are regularly supplied with the requisite amount of fresh 

 meat, the transformed Amblystomas are very much larger and stronger 

 than those which are transformed without having received any food. 

 In the case of A. tigrinum — those that received food — the transformed 

 animal would hardly have been lecoguized as the same species 5 they 

 were not only larger, but of a very deep, muddy, black color, without 

 spots, while the others were mottled with bright yellow and a pale 

 brown. 



"(9) The depth of the water has a wonderful intiueuce upon the meta- 

 morphosis ; and the fact is well known that the deeper the water in 

 which the AxDlotls live the slower their transformation. 



"Temperature is another important factor in the change, and its 

 moderate increase seems to hasten the transformation. 



"Now, the most interesting part of all is to watch the operation of 

 these laws that I have given, in nature, and the manner in which the 

 metamorphosis of Axolotls is there effected. 



" It would, indeed, be hard to find anywhere a more perfect and beauti- 

 ful example illustrating the extremely sensitive balance that may exist 

 between the surrounding conditions on the one hand and their effect 

 upon an animal organism on the other. This year, for instance, the 

 pond that I have observed gradually dried up; the north half of it 

 entirely. This took a number of weeks, but during that time all the 

 modifications of which the metamorphoses of Axolotls are subject to 

 or capable of, were, so far as their necessity goes, most lucidly demon- 

 strated. A shallow corner of this pond would, after a torrid day or two, 

 dry up, whereupon all the Axolotls that happened to be caught within 

 its limits would be found — perhaps several hundred of them— under the 

 debris, rapidly assuming the Amblystoma form. 



" Numbers of the same generation, however, in deeper parts, would be 

 unaffected by the change of environment so suddenly precipitated upon 

 their brethren. If the drying up continued, these transformed animals 

 quit the site, and during the next few days could be found under logs, 

 and in other suitable places at some considerable distance from it. On 

 the contrary, should a rain in the mean time fill the pond again and 

 flood over these shallow parts, the transformations were checked, and 

 those with gills and branchiiie in all stages of change once more took 

 to the water. When huddled together in the shallow places, the large 

 and strong ones devoured the smaller and feebler forms 3 and the differ- 



