306 



FISHES 



CHAP. 



V.C. 



septa give to the cavities of the lateral compartments the appear- 

 ance of being occupied by a coarse spongy network. 



() In its relations to the oesophagus and to the air-bladder 

 the ductus pneumaticus exhibits striking modifications in 

 different Teleosts. "With very rare exceptions, an open ductus 

 is wanting in the Heteromi, Catosteomi, Acanthopterygii, Opis- 

 thomi, Pediculati, Jugulares, and the Plectognathi, for which 

 reason the term " Physoclisti " has often been used as a collec- 

 tive name for these Fishes. On the other hand, a permanently 



open ductus is generally pre- 

 sent in the Malacopterygii, 

 Ostariophysi, Apodes, and the 

 Haplomi, which, in conse- 

 quence, have been designated 

 " Physostomi." It must be 

 emphasised, however, that all 

 Teleosts are Physostomous in 



~~ the embryonic condition, and 



whether they eventually be- 

 come Physoclistous or remain 

 Physostomous depends entirely 

 on the abortion or retention 

 of the primitive communica- 

 FIO. 183. Transverse section through the tion between the air-bladder 



abdominal region of Collichthys lucida. 

 a.b, Air-bladder ; d.b and v.b, the dorsal 



and the 



canal. 



mipnTnflHmi<s with a 

 US ' Wlt 



exceptions (e.g. Noto- 



alimentary 



and ventral branches of the air-bladder ; When present ill Teleosts, the 



I, liver ; in, mesentery ; s, stomach ; v.c, 



vertebral column. The dotted and broken 



lines surrounding the bladder and its few 



branches represent the peritoneal invest- f \ wbprp ir is both shorf 



ment of these parts. (From Giiuther.) P lt 



and relatively wide, is almost 



invariably much longer and narrower than in the other orders 

 of Teleostomi and in the Dipnoi, sometimes passing directly from 

 the air-bladder to the oesophagus, but not infrequently describing 

 a sigmoid curve, as in some Cyprinidae, or an even more tortuous 

 course. The opening into the alimentary canal is, with perhaps 

 a single exception, dorsal, but may vary from the commence- 

 ment of the oesophagus to the hinder end of the stomach. In 

 Erythrinus the oesophageal aperture is lateral. In two instances 

 the air-bladder has acquired secondary openings to the exterior, 

 and of these one occurs among the Physostomi and the other 



