1911] Smith, Natural History of Ambystoma. 15 



"Branchipus Pond'' is, in the spring, several acres in extent. 

 On one shore is an almost precipitous hillside, sloping gently at 

 the bottom down to the water line. Near the pond is a shallow 

 ditch, extending at right angles from the hillside. The ditch, and 

 the shore of the pond nearest the hill, are favorite spawning 

 grounds for Ambystoma. 



Besides the two species of Ambystoma mentioned, the follow- 

 ing other species of amphibia occur in the locality : Diemyctylus 

 viridescens, Plethodon erythronotus, Rana pipiens, Rana sylvatica, 

 Hyla pickeringii. In the early spring, just as the ice is melting 

 from the pond, vast numbers of Branchipus sometimes make 

 their appearance ; hence the name of the pond. 



The hillside mentioned is a steep talus, consisting of rock 

 fragments mingled with vegetable mold. This affords a laby- 

 rinth of natural cavities, the ordinary terrestrial dwelling-places 

 of the local urodeles. Here they find abundant food: earth- 

 worms, etc. 



In the vicinity of Ann Arbor, Ambystoma pun datum and A. 

 tigrinum breed in different ponds, each species occurring to the 

 exclusion of the other. I have noted only a single bunch of eggs 

 in exception to this rule. The cause of this phenomenon is a mat- 

 ter for conjecture ; possibly an explanation lies in an adaptation 

 of the structure of the larvae (e. g., presence or absence of "bal- 

 ancers") to certain factors in the environment (e. g., character 

 of the bottom, whether leaves, pebbles or mud, etc.) ; or the 

 larvae, of one species may devour those of the other, or monop- 

 olize the food supply. 



THF, SPRING MIGRATION. 



The fact that A. punctatum winters on land and migrates to 

 water after the opening of spring has been established by Wright 

 ('08). The following observations on this point are in complete 

 accord with Wright's account and point to the same phenomenon 

 in A. jeifersonianum. 



During the fall of 1908 Branchipus Pond was completely dried 

 up. This was noted in the latter part of September. Since dry 

 weather continued until very late in the fall it seems probable that 

 cold weather overtook the Ambystoma before they could have 

 made use of the pond as winter quarters, had it been their habit to 



