328 



MANUAL OF ZOOLOGY 



SECT. 



in all three, apertures 

 will be observed, which 

 serve as the orifices 

 through which the in- 

 testine and the ducts 

 of the urinary and 

 genital organs communi- 

 cate with the exterior. 

 A further resemblance 

 between the Lizard and 

 the Rabbit is seen in 

 the presence of two 

 pairs of jointed limbs, 

 anterior or pectoral, and 

 posterior or pelvic, the 

 principal divisions of 

 which correspond in 

 their general arrange- 

 ment. In the Dog-fish 

 these are found to be 

 represented by very 

 different-looking struc- 

 tures, the paired fins 

 (Fig. 192, pct.f.,pv.f.). 

 At this point all external 

 resemblance ceases, and 

 we see nothing but dif- 

 ferences. 



The skin of the Dog- 

 fish, though almost 

 smooth, is harsh to the 

 touch, and, when we ex- 

 amine it with a lens, this 



