MACKERELS. 
131 
I, still ; as they are said to appear among the 
I Orkney Islands, and in the Frith of Forth about 
the end of July or the beginning of August, 
j It is now generally believed that the whole of 
I the phenomena of the seasonal appearance and 
I disappearance of fishes may be accounted for on 
’ the principle, now pretty well ascertained, that 
the vivification of the spawn requires its deposi- 
! tion in situations where the sun’s rays can have 
I ready access to it. But this would be impos- 
ji sible if it were deposited on the bottom in con- 
I i siderable depths of water ; and hence, these ani- 
mals have been endowed with instincts, which 
I impel them at the proper period, to resort to the 
I shallows of the coast, where the incumbent stra- 
it turn of water is not too great to allow the solar 
ll light and heat to penetrate to the sand and 
i: gravel of the bottom, among which the ova are to 
ji find their resting-place. 
; On this interesting subject we are glad to 
I quote the opinions of one of the most illustrious 
of ichthyologists. It does not appear,” ob- 
serves Mr. Yarrell, to have been sufiiciently 
; considered, that, inhabiting a medium, which 
I varied but little either in its temperature or pro- 
! ductions, locally, — fishes are removed beyond the 
infiuence of the two principal causes which make 
a temporary change of situation ne*cessary. In- 
dependently of the difficulty of tracing the course 
pursued through so vast an expanse of water, the 
order of the appearance of the fish at different 
places on the shores of the temperate and south- 
ern parts of Europe is the reverse of that which, 
according to the theory [of the older naturalists], 
ought to have happened. It is known that this 
