YAWNING OF FISHES AND OTHER VERTEBRATES. 385 



While expecting that more perfect knowledge would show that 

 yawning is also universal among Mammals, I cannot recollect 

 ever having seen Cetaceans of any kind yawning when at the 

 surface of the sea, but that is no proof that they do not do so ; 

 and is it physiologically impossible for mammals, however 

 thoroughly specialized for an aquatic life, to perform this action 

 under water ? Some species of Cetaceans (and most likely all) 

 certainly appear to sleep under water more often than on the 

 surface. The Great Ant-eater would seem the most likely of all 

 mammals to be an exception to the general rule, but it would be 

 safer to assume that even it can yawn until the contrary is 

 proved ; and the same may be said as to the Petromyzontidce 

 among Fishes. 



Of the mammals as to which Mr. Elmhirst expresses doubt, 

 Horses very commonly yawn (one of my farm-horses always 

 yawns directly he finds that he is being " shut out," i. e. 

 released, from the cart, plough, or other implement that he has 

 been dragging or assisting to drag) ; Asses, Cattle, Sheep, and 

 Pigs also yawn. Goats I cannot answer for, but there is not 

 the slightest reason why they should be exceptional. Among 

 rodents, as to which order Mr. Elmhirst can find no record, 

 domesticated Babbits and Guinea-pigs yawn at any rate, and I 

 do not doubt that I have seen other rodents do so also. 



Of the few species of wild mammals with which I am specially 

 familiar, most are certainly yawners ; it seems unnecessary to 

 give a list, and I submit, with all deference, that it is superfluous 

 to publish a catalogue of the vertebrates that are seen to yawn, 

 but rather that any species (or family) should be noted which, 

 after having been kept under careful observation, has never 

 been detected doing so. 



