PAEENTAL CARE AMONG FRESH-WATER FISHES. 



425 



resting on the outspread pectoral fins, whose form is so well adapted 

 to give a wide resting surface. At last they nia}^ deliberately move 

 away, working the pectorals like a fan, the lower rays being the first 

 deflected. If the water is foul, they Avill dart to the surface, take a 

 mouthful of air. and then raj^idly descend to the ground again. It 

 is noteworthy that part of the air gulped down escapes b}^ the spira- 

 cles behind the eyes. 



The name pneumatoccele was coined as a common name for a vis- 

 cus, which may be either an air bladder or a lung— that is, for the 

 primitive diverticulum of the intestine, which was not specialized as 

 one or the other. The pneumatoccele of the Polypterids is double on 

 the floor of the abdominal cavity, and cellular; it is, indeed, a 

 partly united pair of lungs, rather than 

 an air bladder, and acts as a lung and not 

 as a hydrostatic organ or air bladder. 

 The emission of air instead of water 

 through the spiracles is in harmonv with 

 this function as a lung. This approxima- 

 tion of the Polypterids to amphibians by 

 its respiratory function is coordinate with 

 another character of amphibians. In 

 typical fishes the main instrument of pro- 

 jDulsion is the tail and caudal fin, and the 

 pectorals chiefly preserve its equilibrium ; 

 in the Polypterids the ]oectoral fins 

 assume a large share in the function of 

 progression, supplementing the caudal. 



Although provided with real lungs, 

 Polypterids do not appear to be able to 

 live long out of water. At least Harring- 

 ton complains that they " will not survive more than three or four 

 hours out of water, and only then under the most favorable condi- 

 tions — that is, covered with damp grass and weeds." This feebleness 

 was a great obstacle to success in getting mature eggs and sperm at 

 the same time. 



Another characteristic in the actions of the Polypterids has been 

 recorded by Harrington. '' Peculiar in the swimming movements " 

 is "the manner in Avhich the head moves freely from side to side. 

 This produces the appearance of a progression more or less snake or 

 eel-like, although in general the powerful sweeps of the strong tail 

 characterize the progression as fish-like." 



The food of the Polypterids is limited by their ability of locomo- 

 tion and ingestion; it consists mainly of small fishes and amphibians 

 as well as crustaceans, but the variety is liberal. Harrington found 

 that besides small catfishes, such as the " armoot, bayad, schilbe, and 

 SM 1905 — —31 



Fig ll.—rulyptcrus bichir. After 

 Geoffroy Saint-Hilaire. 



