CLASSIFICATION OF TELEOSTEI. 521 



without nervous matter. The optic nerves are remarkable, 

 because they cross one another without fusing (decussate). 

 As in Ganoids, the partitions between the gill-clefts dis- 

 appear ; so, instead of the pouches seen in Elasmobranchs, 

 there is, on each side, one branchial chamber, covered over 

 by an opercular fold. Into this chamber the gill lamellae 

 borne by the branchial arches project freely. In most, a 

 swim-bladder is developed from the dorsal side of the gullet. 

 There is no spiral valve in the intestine, and the food canal 

 ends in front of, and separate from, the genital and urinary 

 apertures or aperture. The base of the ventral aorta is 

 swollen into a non-contractile bulbus arteriosus, but there 

 is no conus, unless very exceptionally, as in Buthyrinus. 

 According to some authorities, the archinephric duct is 

 unsplit, and there is no Miillerian duct ; according to 

 Jungersen, the oviduct is a true Miillerian duct. The 

 pronephros degenerates ; the ova are numerous, and are 

 fertilised in the water. 



Classification of Teleostei (after Giinther). 



f Acanthopteri. Example — Perch. 

 Dorsal, anal, and pelvicl 



fins in part spiny. j Pharyngognathi. Example. — 



I. Wrass. I Physoclysti, — duct 



(\ of swim-bladder is 

 closed. 



a t ,lt1 "' I Physostomi : duct of swim-bladder remains open. Ex- 



\, amples. — Herring, Salmon, Carp, Eel. 



Besides these chief sub-orders, there are two sets of aberrant forms : — 

 (a) The sea-horses, such as Hippocampus and Phyllopteryx , and the 

 pipe-fishes, such as Syngnathus, are distinguished as Lopho- 

 branchii. The gills, instead of being rows or filaments, are 

 tufts of rounded lobes ; the gill-cover is a simple plate, leaving 

 a small aperture ; the skin is more or less protected by large 

 dermal plates ; the toothless mouth is at the end of a pro- 

 longed snout ; the swim-bladder has no duct. 

 (J>) The globe-fishes, such as Tetrodon and Diodon, the trunk-fishes— 

 Ostracion, the sun-fish — Ortkagoriscus, and others, are distin- 

 guished as Plectognathi. The body is globular or compressed 

 sideways ; the skin bears bony scutes or spines, or is naked ; 

 the skeleton is incompletely ossified, and the vertebra are few ; 

 the bones of the upper jaw are more or less fused ; the pelvic 

 fins are absent or reduced to spines ; the gills are comb-like ; 

 the swim-bladder has no duct. 



