70 J. W. SLATER, ESQ., P.C.S., F.E.S., ON 



one about the hearing apparatus of insects. It is no doubt 



difficult to suppose that the hearing apparatus lias been turned 

 from place to place in the course of development; but the hearing 

 of insects is in a very rudimentary condition, and I imagine that 

 Avhen the sense of hearing first began to show itself, it would be 

 by some parts of the body becoming more sensitive than other 

 parts to sound waves ; and it might be naturally supposed that 

 this beginning would take place in various parts of the body, and 

 that, afterwards, those rudimentary organs of hearing would be 

 improved by natural selection which were in the most convenient 

 place. But with regard to development generally, as has been 

 pointed out this evening, the theory of natural selection seems to 

 found itself on chance — the idea that chance variations take place 

 and that then these chance variations are impi'oved and confirmed 

 when found to be useful. I think a very strong argument might 

 be brought against this. A chance variation would be single, 

 and there is no reason why, when a variation takes place by chance, 

 two or three variations should take place at the same time, having 

 a definite reference to each other. But it can almost always be 

 shown that a mere single chance variation would be no advantage 

 to the creature. Take such a case as the development of the 

 power of flight in a bird. Supposing that, a bird was born with a 

 longer wing than the species usually had ; if this were merely the 

 result of chauce there would be no reason why both wings should 

 be longer — why not one only ? But passing this by, and sup- 

 posing they were both longer, still that would be of no advantage 

 to the bird unless the muscles were also stixmger in proportion, 

 and then they would require a stronger attachment, so that it not 

 only requires longer wings, but also a modification in the muscles 

 and breast bone and possibly also in the breathing apparatus, all 

 corresponding together in order that the bird may gain any 

 advantage by it, and it is not credible that all these variations 

 should occur together by mere chance. That opens up a further 

 question upon which I should be glad if anyone would throw any 

 light. It is often said by *he advocates of natural selection that 

 acquired variations are not perpetuated. I always ask everyone 

 who knows anything about development, whenever I get the 

 opportunity, what their opinion on that point is ; I have asked a 

 good many doctors and men who are expected to know something 

 about it, and have very often received the answer from them that 



