18 NATURAL SCIENCE [July 



setae, a rich secretion of slime by the epidermal cells, and a 

 somewhat similar method of feeding. It was this last fact which 

 definitely rivetted my attention. It is true that it appears trivial 

 enough at first sight, but the longer it is considered, the more 

 weight does it seem to me to possess. 



Described in general terms, both the leech and the cyclostomes 

 attack living prey by their mouths, and bite into it with buccal 

 teeth. I cannot recall a single other instance of this method of 

 feeding, the nearest approach to it being that of certain molluscs 

 which seize their prey with the radula. Elsewhere, we have limbs 

 modified into jaws in abundance, or pincers, or protrusible pro- 

 boscides shot out and drawn back with the prey adhering ; or, 

 again, tentacles capture food, or simple cilia set up currents of 

 water and sweep particles of food into the mouth ; but only in the 

 leeches and the lower vertebrates do we have, so far as I know, the 

 seizing of living prey in the manner described. 



It may perhaps be remembered that I have already, on several 

 occasions, expressed my conviction that the profoundest morpho- 

 logical transformations leading to the rise of new groups of 

 animals can be traced to the adoption of new methods of 

 feeding. This appears to me such a self-evident proposition 

 that it ought to be almost unnecessary to repeat it, 1 yet I am 

 not aware that it has ever been applied systematically except in 

 the two cases in which I have myself endeavoured to apply it. 

 My maiden zoological treatise 2 (apart from a small preliminary note) 

 was an endeavour to show that the primitive crustacean, whose 

 nearest existing relative is Apus, could be deduced from a chaetopod 

 annelid by its adoption of a browsing manner of life in such a way 

 that it could use its parapodia for pushing food towards and into its 

 mouth. I endeavoured to show that the new and richer food-supply 

 which this co-operation of limbs and mouth yielded gave rise to a 

 new race, which could be shown to include not only all the existing 

 Crustacea with their marvellous wealth of varied forms adapted to 

 almost every conceivable environment, but also the trilobites and 

 the Gigantostraca. The somewhat hostile reception accorded to 

 this little work (which, no doubt, for many subsidiary reasons, it 

 deserved), did not shake my conviction that the principle adopted 

 was sound, and that, in order to understand the essential morphology 



1 One objection suggested to me is, that the proposition assumes the in- 

 heritance of acquired characters. On this point I have already stated my views 

 (Nature, vol. I., p. 546. 1894), hut in the meantime it is worth asking whether it 

 really does assume anything of the kind. Say that new pastures call for a new method 

 of feeding, which, again, requires certain structural adaptations, can the rise of the 

 latter not be explained by a process of natural selection, the new requirements for 

 success in life weeding out all whose congenital variations were not in the required 

 direction ? For my own part, I can see no difficulty in believing in inheritance. The 

 objection as to the absence of proof begs the question as to what is meant by proof. 



2 The Apodidae. Nature Series. London : Macmillan & Co. 1892. 



