Relation of Higher Animals to Man 549 



From such a standpoint it will clearly appear that each of 

 the five above-mentioned lines of animal progression approach 

 — though by varying degree — much more nearly to man, than 

 do others that started at the same level with them in the ani- 

 mal scale, but which, from environal action and proenvironal 

 response, have lagged behind in the sweep of evolutionary 

 advance. 



Since in all of the bilaterally arranged animals the brain is 

 placed anteriorly, those organs or appendages which can come 

 in contact with environal stimuli most richly can most eco- 

 nomically be aggregated round the head. Furthermore, if 

 any structures or appendages, by proenvironal action, become 

 increasingly utilized for conveying a variety of stimuli to the 

 brain, or for conveying motor impulses from it, on the dynam- 

 ical law of "action and reaction" the brain and accessory head 

 appendages whether they be antennae and mandibles, or ten- 

 tacles, or forelimbs as a whole, or hands, will reciprocally affect, 

 and be affected by stimuli from, these appendages. 



If such principles be true, they should receive marked con- 

 firmation from study of the five or six above-named series of 

 animals that have run ahead of most genera of their natural 

 groups. These will now be examined for that end. 



The Cephalopoda represents a very ancient group of mol- 

 luscs, abundant representatives of which can be traced from 

 the ordovician and silurian systems up to our day. The genus 

 Nautilus, that is still alive, is closely related to forms that show 

 such geologic range. In all of these the arms or tentacles re- 

 sult from forward growth of the muscular foot round the head, 

 and subdivision of this into lobes. These lobes in Nautilus 

 may be 90 or more, are smooth, and are devoid of hooks or 

 suckers. Their function is — as in the feelers of the snail — tac- 

 tile, apparently chemo- and mechanotactic for food material, 

 while the strong shell has served as a protective covering. 



But gradually, in genera of the group, the arms have become 

 equipped with hooks or suckers or both, and have become re- 

 duced in number till now 10 or 8 are alone develojied in other 

 surviving genera. But these have become highly specialized 



