Wallich, on Microscopic Objects. 
83- 
a locality from which we might naturally anticipate highly 
interesting gatherings. But, beyond the tidal influences, 
the Diatomaceous forms of Bengal are peculiarly general. 
Indeed, along the entire Gangetic valley, they may be said to 
be so — a circumstance in all probability resulting from the 
extensive character of the annual inundation, which, sweeping 
across river and plain, converts the entire surface of the 
country, at times, into a vast inland sea, and of course 
favours the distribution of each minute organism throughout 
the entire range of its occurrence. 
During the rains also, as the mountains contribute largely 
to these inundations, it is not to be wondered at that forms 
detected in the hill lakes and rivulets gradually find their 
way down into the plains below, and by degrees become 
acclimatized there. Indeed few species occur in the moun- 
tain lakes, such as those about Nynee Tal and Almorah, that 
are not also to be found in the plains. But it is remarkable 
that one well-defined species, which occurs somewhat sparingly 
in the lakes referred to, is completely lost sight of throughout 
the entire length of the Gangetic Valley, and reappears, 
strangely enough, in profusion amidst the brackish channels 
of the Sunderbunds, at a distance of 1200 miles. 
Another species, well known in this country, and, if 1 
apprehend aright, frequenting only brackish w^ater, is not 
only common to the plains of Bengal, but presents itself in 
the same mountain lakes, and also in the primaeval wilderness 
of the Delta. 
I mention this fact to show under what widely differing 
circumstances species may exist, and still retain their specific 
characters unimpaired ; and that the mere fact of a peculiar 
habitat may not, after all, be so useful in determining species 
as has by some observers been laid down. 
My marine gatherings, I would mention, were made during 
the voyage round the Cape, in a sailing ship, under peculiarly 
favorable circumstances to the microscopist, though not so 
to the navigator ; inasmuch as frequent calms, both in the 
Bay of Bengal, Indian Ocean, on the Lagalkas Bank to the 
southward of the Cape, at St. Helena, and off the W estern 
Isles, aflPorded constant opportunities for using the casting 
net, towing net, or dredge, as the case might be. 
Of course, from the open sea, the purely microscopic forms, 
with a few exceptions, could only be obtained by having 
recourse to the floating living creatures of various kinds that 
abound on the surface, under certain circumstances, in almost 
every latitude. It was only w^hen going rapidly through the 
water, that is beyond five or six knots an hour, thai it 
