154 SPINOUS FISHES. 



rant fertilit}', that the herring, the pilchard, and fome 

 others, are obliged to migrate annually, from the artic 

 regions, in fhoals of fuch vail extent, that for iplles they 

 are feen to darken the furface of the water. 



But the amazing propagation of filhes, which we wlt- 

 nefs alpng our coafts and rivers, bears no proportion to 

 the vail quantities that fwarm in the warmer latitudes of 

 the Indian ocean. The Inhabitants of fome of the iflands 

 there, are, it is faid, under no neceflity of providing in- 

 ftruments for filhing : As> they approach the fhore, they 

 are found in great numbers, in the plafhes, where the 

 water remains after the ebbing of the tide. In fome 

 places where thefi;j fwamps are dried up by the fun, the 

 fifties are left in fuch ihoals, that they communicate by 

 their putrefa^ion, a noxious and unhealthy tindiure to 

 the atmofphere. 



Happily, however, for the purity of that element, and 

 the health of thofe beings which it fupports in life, the 

 wafle of thefe fifties is nearly proportioned to their fecun- 

 dity ; amd the balance of nature is exaftly preferved. 

 The fhark, the porpefTe, and the cod, we ought there- 

 fore to confider not fo much in the light of plunderers and 

 rivals, as that of benefaftors to mankind: Without 

 their exertions, the fea would foon be overcharged with 

 the burthen of its own inhabitants ; and that element, 

 \vhich at prefent diftributes health and plenty to the 

 Ihore, would in a ftiort time load it with putrefaction *, 



The generation and growth of fifties, and particularly 

 of the oviparous, are involved in great obfcurity. The 

 common opinion, as we have already ft:ated, is, that im- 

 pregnation 



* {dsm ubi fupi> 



