OF Ci^RTILAGINOUs FISHES. S5. 



■Silrk tribe 5 and among a third clafs, they are fituated on 

 the top of the head, as exemplified by the pipe fifh. 



From thefe foramina, there are two bending cylindri- 

 cal dufts, that run to the lungs, and arefuppofed to con-f 

 vey the air that gives their organs their proper play : 

 The heart, however, has but one valve ; and hence, their 

 blood does not perform that double circulation which ob- 

 tain among the cetaceous kinds, and the lungs feem ra- 

 ther an internal afliilant to the gills, than for fuppiying 

 the fame purpofe which they do in quadrupeds, for they 

 want both the pulmonary vein, and artery. 



Another ftriking charafter by which this order of the 

 animal kingdom may be diftinguifhed, is, that their fleih 

 is fuoponed by cartilages inftead of bones. In the ceta- 

 ceous tribes we have feen, that the bones were hard, and 

 filled with marrow, refembling thofe of quadrupeds, 

 while thefe parts in tiie fpinous tribes, are fmall, {lender, 

 and pointed, refembling thorns, and generally folid 

 throughout. The fize of other animals increafes with 

 their age, and flops at a certain point ; but from the pli- 

 ancy of the bones in this tribe, they feem to have no 

 bounds placed to their diraenlions, and it is fuppofed 

 that they grow larger every day till they dief. 



A third general character of thefe fi(hes arifes from 

 their manner of generation ; fome of them are oviparous, 

 while the greater part produce living young ; the fame 

 duplicity of character attending them in this refpect, 

 which we have already taken notice of with regard to 

 their conformation. In thofe that are viviparous, the 

 progeny is excluded from an egg hatched within the bo- 



dy 



f Goldfjnith's Nat. Hul. vol. a, p. 2 31* 



r 



