18701882] HYATT AND COPE 343 



certain degraded characters appearing in the last species Letter 254 

 of a series. You ask for my opinion : I can only send the 

 conjectured impressions which have occurred to me and which 

 are not worth writing. (It ought to be known whether the 

 senile character appears before or after the period of active re- 

 production.) I should be inclined to attribute the character in 

 both your cases to the laws of growth and descent, secondarily 

 to Natural Selection. It has been an error on my part, and a 

 misfortune to me, that I did not largely discuss what I mean 

 by laws of growth at an early period in some of my books. 

 I have said something on this head in two new chapters in 

 the last edition of the Origin. I should be happy to send 

 you a copy of this edition, if you do not possess it and care 

 to have it. A man in extreme old age differs much from a 

 young man, and I presume every one would account for this 

 by failing powers of growth. On the other hand the skulls 

 of some mammals go on altering during maturity into 

 advancing years ; as do the horns of the stag, the tail-feathers 

 of some birds, the size of fishes etc. ; and all such differences 

 I should attribute simply to the laws of growth, as long as full 

 vigour was retained. Endless other changes of structure in 

 successive species may, I believe, be accounted for by various 

 complex laws of growth. Now, any change of character thus 

 induced with advancing years in the individual might easily 

 be inherited at an earlier age than that at which it first 

 supervened, and thus become characteristic of the mature 

 species ; or again, such changes would be apt to follow from 

 variation, independently of inheritance, under proper con- 

 ditions. Therefore I should expect that characters of this 

 kind would often appear in later-formed species without the 

 aid of Natural Selection, or with its aid if the characters were 

 of any advantage. The longer I live, the more I become 

 convinced how ignorant we are of the extent to which all 

 sorts of structures are serviceable to each species. But that 

 characters supervening during maturity in one species should 

 appear so regularly, as you state to be the case, in succeeding 

 species, seerns to me very surprising and inexplicable. 



With respect to degradation in species towards the close 

 of a series, I have nothing to say, except that before I arrived 

 at the end of your letter, it occurred to me that the earlier 

 and simpler ammonites must have been well adapted to their 



