THE VPSILOID APPARATUS OF URODELES. 2/p 



air. This is immediately followed, as the head again returns 

 into the water, by a forcible swallowing motion as a result of 

 which the air is forced from the mouth partly into the lungs and 

 partly out through the nostrils. Of those spe'cies the habits of 

 which I have studied, Dicuiyctylus viridescens accomplishes with 

 the greatest ease the act of taking air into the lungs in this way, 

 an observation quite in harmony with the fact that Dicmyctylus 

 has the reputation of being the most thoroughly aquatic of our 

 American salamanders. 



The Gages ('86tf, r) have shown that, in general, an animal 

 having a mixed aquatic and aerial respiration depends mainly 

 upon the latter for its supply of oxygen. I am not convinced, 

 however, that this is of necessity true in the case of lunged sala- 

 manders living under aquatic conditions. Diemyctylus and the 

 Amblystomas, it is true, not only swim frequently to the surface 

 and take in air, but, if it is possible, will partly crawl out of the 

 water and for a shorter or longer time each day will breathe air 

 normally. However, to test the absolute physiological necessity 

 for aerial respiration, I experimented as follows : Several speci- 

 mens of Diemyctylus were enclosed in small wire cages which 

 were immersed to a depth of about 15 inches in a small tank of 

 running water. To prevent the collection of bubbles of air upon 

 the inside of the wire, the cages were frequently shaken to remove 

 the bubbles while they were still too small to be used in breath- 

 ing and thus vitiate the experiment. To ensure this frequent 

 agitation during the night when personal attention to the matter 

 was inconvenient, I used the simple device of placing a large 

 and lively specimen of Necturus in the tank with the cages. The 

 Nectiinis, being nocturnal in its activities, accomplished quite as 

 efficiently the duty of keeping the cages free from air as was 

 done during the day time by my own exertions. The precaution 

 was taken, moreover, to make it impossible for any activity of 

 the Necturus to lift the cages out of the water. 



For periods varying from seven to ten days specimens of Die- 

 myctylus were thus kept completely submerged and they remained 

 in an active condition and apparently suffered no inconvenience as 

 a result of the experiment. The capillaries of the skin, however, 

 as observed by means of a lens, were much more distended with 



