60 



THE AMERICAN NATURALIST [Vol. XL 



withstanding the objections just mentioned to the possibihty of 

 a smelling function. This possibility becomes a probability if 

 not a reality by the observations on the manatee given above. 

 From these observations it follows that in the Sirenia, at least, 

 there is no connection between the reduction of the exethmoids 

 and that of the olfactory nerve as there may be in case of the 

 whales. It is also clear that the olfactory nerve as a functional 

 structure must be capable of perceiving chemical stimuli that 

 utilize water as -the carrying medium instead of air as with land 

 mammals. This assumption, of course, implies not only a par- 

 tial functional adaptation of the olfactory nerve but it also limits 

 such an adaptation to the herbivorous Sirenia alone. Finally we 

 must also assume that the chemical stimulus, since it cannot 

 reach the olfactory membrane in the usual way, must take another 

 course, perhaps by way of the mouth, pharynx, and choanes. 



One more observation on the reflex irritability of the nasal 

 membrane may be added here. Before the death of the captive 

 dugong, Dexler endeavored to squirt w^ater into the animal's 

 nose as it drew in a breath. Instantly there came so violent an 

 expulsion of the fluid — which had barely entered the nostril — 

 that it was blown into a fine spray. The reflex was astonishingly 

 violent and quick, and after it had taken place the nostril open- 

 ings were fast closed as before. Thus the breathing movement 

 that had been begun, was not completed. Surely so prompt a 

 reaction is of the greatest importance for aquatic mammals. 

 The action by which the nose is closed in case of the dugong is 

 thus two-fold: voluntary and reflex. Water pressure as an aid 

 is not necessary, or at least only auxiliary. 



The dugong's sight must be characterized as rather poor. 

 Otherwise it wwld be impossil)le to caj)ture the animal with 



to 150 meters long and from T) to (> meters dee]) are so disposed 



easily on clear nights and for this reason the best time to take 

 them is during the nights of the new moon. The cords of the 



