MANUAL OF NATURAL HISTORY. 85 



many will encounter and overcome apparently in- 

 surmountable obstacles. In ascending streams, Sal- 

 mon and Trout take often wonderful leaps, clearing 

 thereby small rapids and falls. The former species 

 leaps farther and higher than the latter, which is 

 used to measure the size and strength of falls in some 

 North American rivers, a Salmon leap being more 

 considerable than a Trout leap. At present consider- 

 able attention is being paid to the artificial impreg- 

 nation of fish-roe, a process which promises to prove 

 of no little importance. 



The most simple and primitive division of fishes is 

 into osseous and cartilaginous, according to the na- 

 ture of the skeleton. This was done by Cuvier, who 

 sub-divided the former from the nature and position 

 of the fins. Agassiz, as before stated, proposed a 

 classification founded on the shape and structure of 

 the scales, which, however, being founded on one par- 

 ticular system, may be looked on as somewhat artifi- 

 cial. In the following arrangement, the orders have 

 been taken from Professor Owen's modification of 

 Miiller's classification; while the descriptions of fami- 

 lies are mostly from Cuvier and Swainson. The more 

 comprehensive families of Muller and Owen, however 

 perfect in a philosophical point of view, or however 

 well adapted for a work including mention of ge- 

 nera, are not suited for our pages, as they would 

 afford but little assistance to those most likely to 

 require directions. The details have therefore been 

 more amplified than they would otherwise have 

 been. The terms " Endo-skeleton" and " Exo- 



