CHAPTER I 



INSECTS AND THEIR NEAR RELATIVES 



PHYLUM ARTHROPODA 



The Arthropods 



Zoologists recognize at least twelve great groups or phyla of animals, 

 — Protozoa (one-celled animals), Porifera (sponges), Ccelenterata (hy- 

 dras, sea-anemones), Platyhelminthes (flatworms), Nemathelminthes 

 (roundworms), Trochelminthes (rotifers), Molluscoidea 

 (lampshells) , Annulata (earthworms, et al.), Echinoder- 

 mata (starfish), Mollusca (clams, oysters), Arthropoda 

 (spiders, insects), and Chordata (fishes, birds, mam- 

 mals). In organization and development the phylum 

 Arthropoda, stands high in the series as indicated in the 

 foregoing linear arrangement. Indeed, the arthropods 

 stand next to the fishes, reptiles, birds and mammals, 

 the highest forms in the animal kingdom. 



If an insect, a spider, a scorpion, a centipede, or a 

 lobster be examined, the body will be found to be com- 

 posed of a series of more or less similar rings or seg- 

 ments joined together; and some of these segments 

 will be found to bear segmented legs (Fig. i). All the 

 animals possessing these characteristics are classed to- 

 gether as the phylum Arthropoda. 



A similar segmented form of the body is found 

 among worms; but these are distinguished from the 

 arthropods by the absence of legs. It should be re- 

 membered that many animals commonly called worms, 

 as the tomato-worm, apple-worm, etc., are not true 

 worms, but are the larvae of insects (Fig. 2). The earthworm is the 

 most familiar example of a true worm. 



In the case of certain arthropods the distinctive characteristics of the 



Fig. 1. — An insect 

 showing segmented form 

 of body. 



Fig. 2. — Larva of butterfly, Papilio thoas. 



phylum are not evident from a cursory examination. This may be due to 

 a very generalized condition; but in most instances it is due to a second- 



