LOWER OLD RED SANDSTONE OF SCOTLAND. 351 



waves or strong currents, would infallibly perish. For it is 

 a fact of which every angler who, in killing his salmon, takes 

 care to keep its head down the stream, is well aware, that 

 fishes can be as certainly drowned in their own element by 

 reversing the course of the respiratory current, and sending 

 It through the gill-opemnga ro the mouth, as any of the air- 

 breathing vertebrata by ordinary immersion. Nature, how- 

 ever, imparts the necessary solidity to the soft abdominal 

 parts ; and this, not by the introduction of a new bit of 

 mechanism into the ichthyic skeleton, — for she is always 

 chary of introducing new pieces into her machine, — but by 

 altering, adapting, and imparting a new function to a pre- 

 viously existing piece. Such is the mode, 1 say, in which 

 Nature works. Let us remark, by way of illustration, how 

 many various functions, as we ascend in the scale of verte- 

 brate existence, we find her making one little organ — the 

 tongue — perform. In the fish we see it fixed, and not un- 

 frequently teeth-covered. It mayhap serves in this class, — • 

 though, as already remarked, in a very low degree, — as an 

 organ of taste, and forms the base on which certain food-de- 

 taining hooks or thorns are placed. Higher up in the scale 

 we find an insectivorous reptile, — the chameleon, — that re- 

 quires a javelin-like organ, with which to strike down and 

 seize its light-winged prey. It receives, not a new organ, but 

 a moc'ification of an old one, — the tongue ; and the required 

 javelin is placed at its command. Higher still we perceive 

 that the herbivorous mammal stands in need of an organ 

 with which to turn round its food in its mouth, so that the 

 giinders may be brought to bear upon every portion of it in 

 succession. And here another modification of the tongue 

 takes place, and the mammal is furnished, in consequence, with 

 the necessary organ. We go higher still. It is essential that 

 thinking, reasoning man have an instrument of speech by 

 which to convey his thoughts In words, and give expression 



