2 The Structure and Special Physiology of Insects 



Of all entomologists, students of insects, the very large majority arc 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 start'ishes, 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- 

 pixla; and any one may readily see — it is most plainly seen in such forms as 

 a locust, or dragon-fly, or butterfly, and less ])lainly 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, 



