252 Transactions. — Miscellaneous. 



is provided ; it then pushes itself upwards by straightening 

 the tail, while it closes its gill-covers so as not to prevent 

 progress, and so on. Now, any perch with unusually large 

 gill-covers or a more muscular tail than ordinary would get 

 on best in this new pursuit ; but before such a modifica- 

 tion of structure could be of any use some particular perch 

 or variety of perch must have been strongly moved with 

 desires which led it to depart from the ordinary habit of 

 its knid and to leave the water and climb palm-trees. In 

 Australia rabbits have learned to climb trees — a habit which, 

 if it becomes hereditary, may give rise to a new species of 

 rabbit. 



The varying habits of different species of spiders will 

 illustrate my argument. There are spiders w^hich construct 

 webs for the capture of prey ; spiders which do not construct 

 webs, but make nests below the surface of water, and there 

 lie in wait for their prey ; others hunt their prey on the land ; 

 others, again, make nests provided with trap-doors, and so 

 on. All these spiders with different habits likewise differ in 

 their physical structure, and form well-marked species. Can 

 it reasonably be doubted that the cause of their original 

 divergence from the common stock was the mental idiosyn- 

 cracies of individual spiders leading them to strike out new 

 lines of life for themselves, their bodily structure and habits, 

 in course of time, becoming fitted for the capture of prey in 

 different ways? If it be conceded that animals do possess 

 mental faculties, and that their actions are, if only to some 

 extent, controlled by those faculties, it seems to follow as a 

 necessary consequence that the mind of the animal must 

 play a conspicuous part in the evolution of a species. 



In the foregoing remarks I have opened up a large subject, 

 to the further consideration of which I may invite the Insti- 

 tute's attention on some future occasion. You will, of course, 

 perceive that, if my views be correct, a cause which has 

 materially influenced the development of animals is absent in 

 the case of plants, although evolutionists have hitherto dealt 

 with the development of animals and of plants as if the two 

 had proceeded on similar lines. 



