To most people the animal kingdom is comprised chiefly of those animals commonly met with in everyday life or in general reading--the game and domestic animals and the fishes, all of which are similar in that they possess a backbone or vertebral column, and are consequently known as the vertebrates. Popularly, however, they are generally classed as the “lower” and “higher” animals; there is certainly some accuracy in such a haphazard classification, since, though all the vertebrates are, strictly speaking, the “higher” animals, some are “lower” (_e.g._, fish, frog, and bird) than others (_e.g._, kangaroo, dog, and man, the highest of all). But when it comes to the true “lower” animals, that vast assemblage of less conspicuous creatures, the jelly-fish and corals, worms of all kinds, sea-urchins, crayfish, wood-lice, spiders and insects, shell-fish and snails, all characterised by the absence of a vertebral column and known as the invertebrates, they are not collectively visualised in a general sense as are the vertebrates. As a rule, these invertebrates are known individually as independent units, except, perhaps, in the case of worms, insects, spiders, wood-lice, etc., which are very often collectively and haphazardly referred to as “insects,” a term, in this sense, as ill-defined as it is unlimited. That the average person should be more conversant with the vertebrates than the invertebrates is, to a great extent, the natural outcome of association and training; a possible influence is to be found at the outset of one’s career in the many illustrated nursery books depicting game and domestic animals, but seldom, if ever, any of the invertebrates; and this impression tends to be further fostered in later life by visits to the zoo, where we meet in person most of the nursery book animals, and perhaps some of the lower forms, such as insects; but the latter, in most cases, are there by chance, not design, and against the will of the authorities.