NATURAL HISTORY. 
mals, are but imperfectly known ;—the latter, often 
appear to be very singular, and complex. As the 
temperature of the medium by which they are sur- 
rounded, is much less subject to variation than that 
of the air, that has perhaps, but a very secondary 
influence, (if any,) on their migrations, and the twe 
great regulating causes probably are, the want of 
adequate and suitable food,—and of a proper situa- 
tion for depositing their spawn. Most ef the deep 
water species, approach the shores in the breeding 
season, and many, as the Salmon, and others, ascend 
far up rivers, and overcome surprising obstacles, 
impelled by that Law of Nature which prompts them 
to continue their species ;—whilst in a few others, 
these movements are reversed, and tho’ habitually 
living in fresh water, their spawn is deposited in 
the sea. 
The Sword Fish, (Xipuias,) Trumpet Fish, 
(Centriscus,) Flying Fish, (Exocetus,) Pilot 
Fish, (CENTRONOTUS,) and a few others, have 
we believe been recorded as occurring in the British 
Channel ;—but they can only be considered as rare 
and accidental visitors, 
