THE TELEOSTEI. 143 



titating membrane, but immovable external eyelids may be 

 develojDed. The choroidal gland, mentioned above, surrounds 

 the optic nerve between the sclerotic and the choroid. Very 

 generally, 2, falciform process of the latter membrane traverses 

 the retina and vitreous humor to the crystalline lens. This 

 represents the pecten of higher Vertebrata. As in other fislies, 

 the lens is spheroidal, and the cornea flat. The sacculus of the 

 auditory organ contains large sohd otoliths, which are usually 

 two in number — the larger, anterior one, is termed Sagitta ^ 

 the smaller, posterior, Asteriscus. There are always three 

 large semicircular canals. 



The reproductive organs are eitlier solid glands which burst 

 into the abdominal cavity, whence their reproductive elements 

 are conveyed away by abdominal pores ; or, as is more usual, 

 they are hollow organs, and are continued backward into ducts 

 which open beside, or behind, the urinary aperture. 



Some few Teleostei are ovoviviparous (e. g., Zoarces vi- 

 viparus), the eggs being retained in the interior of the ovary, 

 and hatched there. In the male SyngnatJms, and other Lo- 

 phohranchii^ integumentary folds of the abdomen grow down 

 and form a pouch, into which the eggs are received, and in 

 which they remain until they are hatched. 



The young of osseous fishes are not known to undergo any 

 metamorphosis, nor are they provided witli external gills, nor 

 with spiracula. 



Tlie classification of the Teleostei is not yet in a thoroughly 

 satisfactory state, and the following arrangement must be re- 

 garded as provisional : 



1. The Physostomi. — Tliis group contains the Siluroiclei^ 

 the Cyprinoidel^ the Cliaracini^ the Cypyi'inodontes^ the Sal- 

 inonidoe, the Scopelini^ the Esocini^ the Morinyri^ the Galax- 

 icB^ the Cli(p>eidce, the Heteropygii^ the Murcenoidei^ Sym- 

 'branchii^ and Gymnotmi. The air-bladder is almost always 

 present, and, when it exists, has an open pneumatic duct. The 

 skin is either naked, or provided with bony plates, or cycloid 

 scales ; the ventral fins, when present, are abdominal in po- 

 sition. The fin-rays (except in the pectoral and dorsal fins of 

 sundry Siluroidei) are all soft and jointed. The inferior pha- 

 ryngeal bones are always distinct. 



In all other Teleostean fishes the air-bladder is either ab- 

 sent, or devoid of an open pneumatic duct. Hence they are 

 termed, collectively, Physoclisti by Haeckel. 



2. The iVnacanthini, — The body has cycloid or ctenoid 



