2 The Structure and Special Physiology of Insects 
Of all entomologists, students of insects, the very large majority are col¬ 
lectors and classifiers, and of amateurs apart from the few who have “crawl- 
eries” and aquaria for keeping alive and rearing “ worms” and water-bugs 
and the few bee-keepers who are more interested in bees than honey, prac¬ 
tically all are collectors and arrangers. So, as collecting depends on a 
knowledge of the life of the insect as a whole, and classifying (apart from 
certain primary distinctions) on only the external structural character of 
the body, any detailed disquisition on the intimate character of the insec- 
tean insides would certainly not be welcome to most of the users of this 
book. 
That insects agree among themselves in some important characteristics 
and differ from all other animals in the possession of these characteristics 
is implied in the segregation of insects into a single great class of animals- 
Class here is used with the technical meaning of the systematic zoologist- 
He says that the animal kingdom is separable into, or, better, is composed 
of several primary groups of animals, the members of each group possessing 
in common certain important and fundamental characteristics of structure 
and function which are lacking, at any rate in similar combination, in all 
other animals. These primary groups are called phyla or branches. All 
the minute one-celled animals, for example, compose the phylum Protozoa 
(the simplest animals); all the starfishes, sea-urchins, sea-cucumbers, and 
feather-stars, which have the body built on a radiate plan and have no back¬ 
bone, and have and do not have certain various other important things,, 
compose the phylum or branch Echinodermata; all the back-boned ani¬ 
mals and some few others with a cartilaginous rod instead of a bony column 
along the back compose the class Chordata; all the animals which have 
the body composed of a series of successive rings or segments, and have 
pairs of jointed appendages used as feet, mouth-parts, feelers, etc., aris¬ 
ing from these segments, compose the phylum Arthropoda. There are 
still other phyla—but I am not writing a zoology. The insects are Arthro¬ 
poda; and any one may readily see—it is most plainly seen in such forms as 
a locust, or dragon-fly, or butterfly, and less plainly in the concentrated 
knobby little body of a house-fly or bee—that an insect’s body shows the 
characteristic arthropod structure; it is made up of rings or segments, and 
the appendages, legs for easiest example, are jointed. An earthworm’s 
body is made up of rings, but it has no jointed appendages. A worm is 
therefore not an arthropod. A crayfish, however, is made up of distinct 
successive body-rings, and its legs and other appendages are jointed. And 
so with crabs and lobsters and shrimps. And the same is true of thousand¬ 
legged worms and centipeds and scorpions and spiders. All these creatures, 
then, are Arthropods. But they are not insects. So all the back-boned 
animals, fishes, amphibians, reptiles, birds, and mammals are Chordates, 
