

A great hammerhead from the Gulf of Mexico and her litter. Few sharks produce this many young at one time. 



greater proportion of young cartilagi- 

 nous fishes reach maturity for that 

 reason. 



Fertilization is internal throughout 

 the class. Internal fertilization is 

 another mechanism by which the car- 

 tilaginous fishes make up for the small 

 number of eggs produced. The chances 

 of the eggs becoming fertilized are 



much greater when fertilization is in- 

 ternal than w^hen it is external as with 

 most bony fishes. Male chondrichthoid 

 fishes are easily recognized by the 

 presence of a pair of intromittent 

 organs called claspers that arise from 

 the inner margins or bases of the 

 pelvic fins and usually extend beyond 

 the tips of the fins in mature cartilagi- 

 nous fishes. 



SHARKS 



Numbers and General 

 Distribution 



An estimated 300 species of sharks 

 are recognized in the world today. In 

 several instances, especially among 

 the larger, far-ranging species, we 

 have probably described the same 

 sharks under more than one name. 

 There are, however, undoubtedly other 

 species existing that have not been given 

 names as yet, particularly in the deeper 

 sections of the ocean and in the mid- 



water realms which have not been 

 thoroughly investigated. 



A few species, including the Green- 

 land shark and the Pacific sleeper 

 shark, inhabit very cold seas, but the 

 variety and number of sharks are 

 greater in tropical and subtropical 

 waters. Sharks are present in greater 

 variety, and probably also in greater 

 abundance, in moderate depths- -from 

 50 to more than 500 fathoms. Sonne 



