NATURAL THEOLOGY. 329 



anirnal's body, and of pleasure or pain experienced 

 at the time. Thus the incubation of eggs is ac- 

 counted for by the pleasure which the bird is sup- 

 posed to receive from the pressure of the smooth 

 convex surface of the shells against the abdomen, 

 or by the relief which the mild temperature of the 

 egg may afford to the heat of the lower part 

 of the body, w hich is observed at this time to be 

 increased beyond its usual state. This present 

 gratification is the only motive with the hen for 

 sitting upon her nest; the hatching of the chickens 

 is, with respect to her, an accidental consequence. 

 The affection of viviparous animals for their young 

 is in like manner solved by the relief, and perhaps 

 the pleasure, which they perceive from giving 

 suck. The young animal's seeking, in so many 

 instances, the teat of its dam, is explained from 

 its sense of smell, which is attracted by the odour 

 of milk. The salmon's urging its way up the 

 stream of fresh-water rivers is attributed to some 

 gratification or refreshment which, in this particu- 

 lar state of the fish's body, she receives from the 

 change of element. Now of this theory it may 

 be said, — 



First, that of the cases which require solution, 

 there are few to which it can be applied with 

 tolerable probability; that there are none to which 

 it can be applied without strong objections, fur- 

 nished by the circumstances of the case. The 

 attention of the cow to its calf, and of the ewe to 

 its lamb, appear to be prior to their sucking. The 



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