Little need be said about collecting. The objects treated of are so plentiful that no great skill, nor any wealth of appliances, is needed to secure an ample supply. The following remarks on the methods employed at the Illinois State Laboratory for the capture of aquatic insects and larvae are, however, worth quoting:—
‘Insects in vegetation, and on or in the bottom, were taken by means of a dip-net—a net of about equal depth and width attached to a strong semicircular ring, firmly fixed to a long handle, the straight side of the ring being opposite the point of attachment. For the larger and more active forms, a coarser net was used, and for smaller forms one made of finer net proved most durable and satisfactory. To collect from the mud of the bottom, the water immediately over it was violently stirred and then swept with the net. The surface layer of mud was also scooped up in the fine dip-net, and then allowed to wash through, leaving the coarser contents in the net. Insects on the bottom in deep water were secured by using a dredge, and washing its contents through net sieves. The aquatic vegetation, when free from mud, was violently washed in a large pan, many smaller forms being thus dislodged and coming to the surface. Insects occurring in open water were taken in drawing an ordinary towing-net[6].’
Here we have, so to speak, the general principles of collecting. It will be easy to adapt them to particular cases.
In choosing the subjects to be treated of in this little book, some difficulty has been experienced in deciding what to select from the multitude that lay ready to hand. It was felt necessary that the subjects should be connected, since choosing them at random would lead to purposeless work, and so to waste of time and opportunity. After some consideration, the author has decided to take all the examples from the Arthrop´oda—that great sub-kingdom of backboneless animals which includes the Lobster, the Crab, the Sand-hopper and the Woodlouse, the Spider and the Mite, the whole world of Insects and the Centipedes. One cogent reason that influenced this decision was the fact that these objects are exceedingly common, so that there can be no difficulty in procuring material on which to work. There is, perhaps, no other sub-kingdom so full of interest, on account of the many widely different forms, which may be referred to one common plan.
It may possibly appear to some readers that the powers of the pocket lens have been exaggerated. As a matter of fact the material for the book has been gathered by actual observation. The author has seen, with an ordinary pocket lens, the objects here described. If some are shown as they would appear under greater magnification than such a lens would give, this is chiefly for the sake of emphasizing points of interest which might otherwise be overlooked, but which can readily be made out with a hand magnifier, when attention has been drawn to them, and the observer knows what to look for.
CHAPTER II
ARTHROPODS AND THEIR CLASSES.—THE MARGINED WATER BEETLE; THE GREAT WATER BEETLE; THE COCKTAIL BEETLE
Having got together our apparatus, which, as we have seen, need be neither costly nor complicated, the next step will be to acquire some knowledge of the group from which the examples here treated of will be taken—the Ar´thropods, or animals with hollow-jointed limbs. These are the ‘Insects’ of the Linnaean classification, and, for the matter of that, of popular phraseology; for though few people would now venture to call a Lobster an ‘insect,’ we still style some of its near relatives Water ‘Fleas,’ as Swammerdam did two hundred years ago.
The Arthropods form a phylum, or main division of the Animal Kingdom. Above this phylum comes that of the Molluscs, or soft-bodied animals, such as the Oyster, the Snail, and the Cuttlefish. Still higher are the Lancelet, the Sea-squirts, and some few others, that bridge the chasm between the phyla without, and that phylum with, a backbone. And to this last Man himself belongs.
Two reasons contributed to the selection of the Arthropods as a subject for work with the pocket lens: (1) the great interest which surrounds many of the group; and (2) the ease with which specimens may be procured and kept under observation.