4663 



Fishes. 



sufficiently delicate I have no doubt that the principal species com- 

 posing any natural family might be determined a priori by an 

 inspection of the embryo and young: then and then only can 

 Zoology be esteemed a Science. 



Observations made on the proportions which the various segments 

 of animals bear to each other, and to the corresponding structures in 

 other animals, bear me fully out in these views. 



In the fish, what may popularly be called the head includes the 

 organs of prehension, the teeth — and of respiration, the gills. Its size, 

 compared with the other segments of the fish, and with the same 

 structure in other species of the same family and subfamily, will 

 always furnish valuable information as to the character of the fish 

 and its generic relations. The same remark applies to the fins 

 generally; but to each after its own manner, seeing that all the 

 fins do not belong to one system. Tn the table which follows 

 are given the various measurements of three distinct species of 

 trout. 



Table I. 



Salmo 

 estuarius. 



Total length I2f 



Length of head, measuring from snout to posterior 



margin of gill cover 2\ 



Utmost gape 

 From snout to eye 



From snout to pectoral fin 



Length of pectoral fin 



From snout to dorsal fin 



From snout to mort fin 



From snout to pelvic fin 



From snout to anal fin 



Breadth of tail 



From snout to end of maxillary bone 



Greatest depth (immediately anterior to the dorsal 



fin) 



Smallest (anterior to the setting on of the tail) 



2* 



If 



81 



4 



1* 



S. Levensis. 

 in. 



12* 

 2f 



n 

 t 



2* 



n 



4| 



9 



5f 



si 



3* 

 li 



S. Salar of 

 the Tweed, 

 in. 



m 



3* 



H 

 1 



3 



*8 



6* 



9 



6* 



8* 



2f 



If 



2| (or ^th of the whole length). 

 1 





