288 PLAGIOSTOMATA. 



few are stragglers from the Arctic, or else from the warmer regions of Europe 

 or of the Atlantic Ocean. Among them some frequent the open seas, migrating 

 long distances often in pursuit of shoals of fishes ; others, again, more frequent 

 our shores and bays, while but few ascend into our fresh waters, as they are fond 

 of doing up the larger rivers of tropical countries. It has been observed that 

 one of the curious consequences of the construction of the Suez Canal has been 

 the introduction into the Mediterranean Sea of sharks which were formerly 

 almost unknown there. The sharks have proved very destructive to the edible 

 fish, and it is now difficult for fishermen to supply the demand. The teeth with 

 which they are armed give an insight into their character, and the size to which 

 these fishes attain is not always an index as to the ferocity or the reverse of the 

 species ; some of the apparently most powerful sharks having small teeth, demon- 

 strating that, even if they are exclusively carnivorous, the forms of animal life upon 

 which they subsist must be small and weak; while the obtuse teeth of other species 

 are more calculated for crushing shells, Crustacea, and worms than waging 

 war with other fishes.* Their bodies are extensively armed with peculiar scales, 

 each of which has a sort of tooth-like appearance, covered by a coating of enamel. 

 This in some forms is termed shagreen and employed in trades, as for the covering- 

 of small boxes, scabbards of swords, or even for smoothing down wood. Several 

 instances are on record where partaking of shark's flesh or liver is said to have 

 occasioned illness, and even death. Personally I have witnessed no bad effects 

 from it, although I have observed European sailors at sea eat it, and in Bombay 

 it is the common food of the Africans. The liver has been accounted the most 

 unwholesome portion. 



The means of propulsion in the different orders and groups among the British 

 Chondropterygians is varied. For in Ganoids, as the sturgeon, the tail and 

 pectoral fins assist ; in the Chimasra the pectorals and ventrals would appear to 

 act without the assistance of the tail : in the true sharks the tail seems to be the 

 chief means, while in the rays the pectorals alone. 



In some forms of sharks the dorsal fins are armed with spines, which render 

 them dangerous to the fishermen, while they are very destructive to nets ; and it 

 is to be hoped that it may be found feasible to institute off our coasts large fishings 

 for these vermin, when possibly their bodies, livers, or their skinsgpight be turned 

 to some profitable use. In the East the fins are exported to China, where they 

 obtain a good sale, due to the gelatine they yield. 



Among Plagiostomes, when breeding, a congress occurs between the sexes, the 

 arrangement of the sexual organs being somewhat similar to what obtains among 

 the higher vertebrata. The male organs are compact, placed far forwards in the 

 abdominal cavity, while, mostly attached to the ventral fins, are claspers shown to 

 to have intromittent functions. In the females different parts of the oviduct 

 may be functionally modified, for although the ova are fertilized within this oviduct 

 the development of the young is not carried out in invariably the same plan, some 

 being perfected prior to extrusion, while in others the ovum is encased in a 

 horny covering and so deposited in the sea. In these last forms the semi-transparent 

 egg cases, variously known as mermaids sailors or sea-purses, are somewhat in 

 the form of a parallelogram, having a long filament from each corner, which serves 

 for the purpose of attaching them to seaweeds, corallines, rocks, or other suitable 

 objects which prevents their being carried away by the waves and lost prior 

 to the birth of the young. Although the females lay many eggs, only two appear 

 to be perfected at a time. Inside this horny r case the foetal shark lies coiled up, 

 while from its umbilical region depends the umbilical sac from which it receives 

 its nourishment. When the proper time an-ives, the case opens at one end and 

 the young fish emerges. In the other forms wherein the young are produced alive, 

 as in the hounds, Mustelus, one species has a placenta. Larval plagiostomes have 

 external deciduous gills. 



* It has been observed by Mr. Porter (Field, May 20th, 1882), that as the ship " Taranaki " was 

 coming home from New Zealand, and all but. becalmed, a Portuguese man-of-war came floating 

 past. A shark snapped at it ; the latter stung him severely with one of its long feelers, causing 

 the shark to thrash the water with its tail in evident pain. 



