6 DR. A. GtTNTHER ON THE BRITISH CHARRS. [Jan. 13, 



tures, Falcons, Hawks, &c., have been so much destroyed by insects 

 that I have thought it better to throw them away. 



" I remain. Sir, 



" Your obedient servant, 



" J. H. Speke, 

 " Captain Commanding E. African Expedition." 



•' P.S. A Leopard was shot here last night." 



" P. L. Sclater, Esq., 



Secretary, Zoological Society, 

 London." 



The following papers were read : — 



1. Contributions to the Knowledge of the British 

 Charrs. Part II. By Albert Gxjnther, M.A., Ph.D., 

 M.D., F.Z.S. 



(Plates I. & II.) 



Since the publication of my first paper on this peculiar group of 

 Salmonidce* , I have received very valuable materials for prosecuting 

 my researches. The additional specimens show that I have been 

 correct in distinguishing the three British species from those of the 

 Continent and from one another, and that the differences between 

 the young and mature fish of one species may be apparently greater 

 than between individuals of the same age but of two distinct species — 

 the laws according to which the changes in the external form proceed 

 from the young to the mature age appearing to be the same in the 

 different species, as far as our present experience goes. It has been 

 observed, in allied species of insects, that, whilst the perfect animals 

 are so completely alike as to be scarcely distinguishable, their larvae 

 are very different in their external characters, and even in their habits. 

 This is not the case with the Charrs : the young individuals of two 

 species differ as much from each other as the old ones. But in order 

 to find out the distinctive characters of two species, it is always 

 necessary to compare specimens of the same age. This can be ascer- 

 tained by the examination of the generative organs, by the develop- 

 ment of the jaws, and finally by comparison of a series of examples 

 from the same locality, assisted by actual observation or information 

 from persons who have been for years acquainted with the Charrs 

 of a certain locality, and know to what size they attain there. 



Among mammals and birds, difference in the size of full-grown 

 animals is admitted as a specific character, whilst ichthyologists have 

 scarcely ever used it as a distinction between closely allied species, 

 because numerous fishes continue to grow for an almost indefinite 

 period after they have attained to maturity. However, if we should 

 be able to ascertain for a series of fishes the age or the size at which 

 they first attain to maturity, the differences observed might be of as 



* Proceedings of this Society, 1862, p. 37. 



