1. SALMO. 7 



5. The form of the caudal Jin in i>pecimens of a given size, age, and 

 sexual development. 



6. A great development of the pectoral fins luhen constant in indi- 

 viduals from the same locality. 



7. The size of the scales, as indicated by the number of transverse 

 rows above the lateral Hne, — one of the most constant characters. 



8. The number of vertebrce. Considering the great number of 

 vertebra in Salmonoids, the constancy of this character is truly sur- 

 prising. An excess or a diminution of the normal number by two, 

 is of rare occurrence, and generally to be explained by the fact that 

 one vertebra has been abnormally divided into two, two such ver- 

 tebra being considerably smaller than the others^or on the other 

 hand that two have merged into one, which is then unusually large, 

 and provided with two ncui-al spines. We have seen one case only 

 where thi-ee vertebras were luiited. The number of vertebrae can be 

 easily ascertained in specimens destined for preservation in spirits, 

 by an incision made along one side of the fish, a little above the 

 lateral line. 



9. The number of pyloric cqypendages. There can be no doubt that 

 this character may materially assist in fixing a species. We shall 

 see that in some species it varies from 30 to 50 ; but in others, as 

 in the Salmon and Charr, it has been found very constant. If un- 

 expected variations occur, their cause may be found in a partial 

 confluence of the caeca, as we have observed that specimens of 

 S. levenensis (a species normally with from 70 to 90 caeca) had 

 those appendages of unusual width when the normal number was 

 diminished. 



AVe have not thought it superfluous to enter into these details 

 (which will be illustrated by instances in the following pages), in 

 order to show that it is only by a close, long-continued study, and 

 constant comparison of specimens of various ages and from various 

 localities, that one is enabled to find a gaiide through this labyrinth 

 of confusing variations. But when we find that the very same cha- 

 racters by which we are enabled to distinguish European species 

 occur again, though in an exaggerated form, in American Salmonoids 

 (which everybody wiU admit to be of distinct species), our faith in 

 them necessarily becomes slreng-thened ; and we no longer hesitate, 

 in accordance with acknowledged principles in zoology, to represent 

 as separate species those which are distinguished from their congeners 

 by a combination of two or more of those constant characters. It 

 has been asked us whether we believed that the forms recorded here 

 as species were derived from separate or common parents. It is not 

 the task of descriptive zoology to determine this question ; for the 

 present, the facts which should prove a gradual creation of the species, 

 and demonstrate the forefather of a recent foiTQ, are so obscure that 

 any view on the subject must still be a matter of opinion. The ques- 

 tion whether the Trout enumerated below should be regarded as dis- 

 tinct species or not, is perfectly independent of such considerations 

 and no more to be afiected by them than the question whether Salmo 

 and Coregomis are distinct genera. Whenever the zoologist observes 



