86 FISH GALLERY. 



once it has been induced to take the bait, which is a live mussel 

 or cockle left in a position where the fish may be expected to 

 come. The young larval forms are band-shaped and transparent, 

 and shrink considerably in size at the end of the larval stage 

 of existence. 



In Sharks, Lung-fishes, Sturgeons, Gar-pikes and Bow-fins 

 there occurs in advance of the ventricle of the heart a small 

 chamber called the " conus arteriosus," the walls of which are 

 of striped muscle-fibre, like those of the ventricle, and the 

 interior of which is provided with watch-pocket valves preventing 

 the blood from passing back into the ventricle. In Teleostean 

 fishes generally there is no conus arteriosus; the ventral aorta, 

 however, is enlarged at its posterior end, where it comes off from 

 the ventricle, and this part is known as the " bulbus arteriosus .^ 

 Its walls are composed of elastic tissue and plain or unstriped 

 muscle-fibre. In the heart of Albula there is a vestigial conus 

 arteriosus, with striped muscle-fibres, and provided on the inside 

 with two rows of valves, two large ones in the front row, and 

 two large and two small in the second row. Albula is thus 

 interesting as being a connecting link between the Teleostean 

 fishes generally on the one hand and the Astylopterygian fishes, 

 such as the Gar-pike and the Bow-fin, on the other. 

 Mor- The Mormyridee are fresh-water fishes of tropical Africa, of 



y ' curious aspect, and very variable in the form of the head. The 

 scales are small and cycloid ; the mouth is often very small and 

 , in some cases (e. g. Gnathonemus curvirostris, 242) set at the 

 end of an elongated snout ; it is bounded above by the premaxillary 

 bones, which are fused together. On each side of the cranium is 

 a large vacuity occupied by a thick-walled air-vesicle, but in the 

 dried skull having the form of a foramen leading into the cranial 

 cavity and loosely covered by a large, thin lamina of bone, the 

 supratemporal. The gill-opening is reduced to a small slit. The 

 eyes are more or less reduced and are often indistinct beneath 

 a thick, semi-transparent skin ; the brain is large in proportion 

 to the size of the body. In Mormyrus and Gymnarchus and 

 some other genera a feeble electric organ occurs on each side of 

 the tail, formed by a modification of the tail muscles into a 



