4 CHONDEOPTEEYGII. SELACHO1DEI. 



the four anterior ones are lined in front with parallel rows of 

 adherent gills, whilst in the fifth these processes are found solely 

 on its proximal side. Water taken in by the mouth for respiratory 

 purposes passes backwards through the pharyngo-branchial slits 

 into these sacs, from whence it emerges by the external gill- 

 openings or stigmata. The scapular arch, which is suspended to 

 the front part of the vertebral column, divides these respiratory 

 sacs from the abdominal cavity. Although opercular pieces are 

 absent, cartilaginous rings are sometimes present surrounding the 

 gill-openings. 



The size to which these fish attain is not an invariable index to 

 their character, which is better shown by an examination of the 

 teeth with which they are armed. Some powerful forms have 

 small teeth, whilst the obtuse teeth of particular genera are more 

 calculated for crushing shells and Crustacea than for waging war 

 with other fishes. The scales are peculiar, being generally small 

 papillae that have a coating of enamel : this, under the designation 

 of shagreen, is sometimes employed in certain trades, as for covering 

 small boxes or the scabbards of swords, or even for smoothing down 

 wood. The tail-fin is flexible and of great power, terminating 

 much like the blade of an oar, and giving the bearer great facilities 

 in pursuit ; when seizing their prey, if it is large, sharks generally 

 turn on one side. 



When breeding, a congress takes place between the sexes, the 

 arrangement of the sexual organs being somewhat similar to what 

 obtains among the higher vertebrates. The male organs are com- 

 pact, placed far forwards in the abdominal cavity, while attached 

 to the ventral fins are claspers which 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 invariably carried out on 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 such forms as produce their young alive, a modified 

 placenta exists. 



Geographical Distribution. Sharks are spread throughout the seas 

 and estuaries of cold, temperate, and tropical regions, being most 

 numerous in the last ; and some ascend rivers even far beyond the 

 influence of the tides *. They are common along the coasts of 

 India, and some species have a wide range, although they do not 

 appear to descend to any great depth. They seem to scent blood 

 or offal from long distances, but their carrying off human prey is 



* Not only sharks but saw-fishes occasionally reside in pieces of fresh water, 

 when the communication with the sea has been cut off. Professor Meyer 

 (' Nature,' Dec. 30, 1875) remarked on this subject that " an accurate comparison 

 (between marine and freshwater forms) showed no difference at all, and 

 therefore the changed conditions seem to have had no influence on the external 

 features of the species." 



