322 THE ZOOLOGIST. 



Saturday midday to Monday morning. Now, as this tank full 

 of water is exposed to the sun on Saturday afternoon and all 

 Sunday, its temperature rises in summer to 6° or 8° F. above 

 that of the sea, and it is then that I have most often noticed 

 the fishes yawning. I find also that when any individual fish is 

 yawning frequently that the rate of its respiratory action is 

 slower than usual. By respiratory action I mean the intaking 

 of water at the mouth, and its emission through the gill-slits. 

 For instance, I find the average rate for a certain Plaice is 

 thirty-two per minute, and twice when yawning frequently it 

 was as low as twenty per minute. A Dab has an average of 

 about forty-two, and when yawning it was thirty-one. Some- 

 times, however, a fish yawns when the number of respiratory 

 actions per minute is above the average. Cod seem to average 

 about thirty-six per minute, whether yawning or not ; I think 

 they yawn much oftener than any others. 



Whether the psychological infectiousness of yawning holds 

 good among fishes I cannot say. I have certainly seen several 

 yawn frequently, oftener than I have seen one give a single 

 yawn. But this may be explained by the conditions conducive 

 to yawning affecting several of the fish. This action is so 

 suggestive that on seeing it I often start yawning myself. I find 

 that a dog yawning before one induces yawning, although I 

 cannot say that I have ever induced my dog or the fishes to 

 yawn by yawning at them. I suppose human beings are pro- 

 bably more susceptible to such influences than the lower 

 vertebrates. When several of a number of fish are yawning 

 frequently, if one does anything to attract their attention all 

 yawning ceases, e. g. if one performs actions as though going to 

 feed them, they become excited, as when feeding is going to take 

 place, swimming rapidly, following one, and making snapping 

 movements as though seizing food. (From this it is quite clear 

 that fish display an intelligent interest in what goes on outside 

 the tank.) This sudden activity is accompanied by an increased 

 rate of the respiratory action, which I suppose sets up a stronger 

 circulation of the blood, and in this way relieves the sluggishness 

 and its accompanied yawning. 



The following list of the occurrence of yawning among 

 vertebrates may be of interest. In the tanks at Millport the 



