464 



PARENTAL CARE AMONG FRESH -WATER FISHES. 



cessory aerial respiration in these aquatic animals." The atmospheric 

 air is "" introduced by deglutition into their digestive tube, traverses 

 that canal throughout its whole length, and, after escaping by the 

 anus, produces a sort of contiiuuil bubbling in the water." The 

 bubbles thus evacuated contain " a large proportion of carbonic 

 acid," and are " naturally less rich in oxygen than atmospheric air." 

 By " studjnng anatomically the vascular tufts which clothe the walls 



Fig. 39. — Iloplosternuin peclorale. After Boulenger. 



of the intestine in which the air, in passing, loses oxygen and be- 

 comes charged with carbonic acid, M. Jobert ascertained that many 

 of these sanguiferous appendages originate from adjacent veins, in 

 the same Avay as the afferent vessels of a lung." 



The habits of two species of very different genera — H oplosteimvm 

 and Corydoras — have been made known. The chief of these, at least 

 so far as size and economical importance are concerned, is Hop- 

 Josternum. This comprises fishes with a broad head high-arched 

 above and separated from the antedorsal plate by the intervention of 

 tAvo nuchal plates, and the plates behind the head (coenosteons or 

 proscapulas) are broad and continued downward to the breast, where 



Fig. 40. — IlopJositdrnum pivioralv, showing plates between dorsal fin and head. 



the pair are sepr.rated by a narrow naked area. There are more 

 characters differ' ntiating the geiurs from others, but those given are 

 sufficient to distinguish it from its nearest relative, CdUichtJiya^ the 

 name-giving genus of the family. Four species of Hoplostei'num 

 are known, the most northern being the H. littomle^ which extends 

 from Trinidad and Guiana to the Kio Plata. 



