ENTOMOLOGY IN OUTLINE SYSTEM IN NATL'RE. i 



Mollusca, and the latter in the Zoophytes, but they were found to be 

 more nearly related to each other than to the branches in which they 

 had been included and the Molluscoidea was erected for them. 



Mollusca embraces what is commonly known as shell-fish, while the 

 land forms are represented by snails and slugs. 



Arthropoda. This is the branch in which we are especially inter- 

 ested. It is separated into two divisions: the Tracheata and Branchiata. 

 The Tracheata are aerial animals, which derive their oxygen from the 

 air by tracheae or tubes. This division includes insects, myriapods, 

 centipedes, thousand-legged worms, etc., and the Arachnida (spiders, 

 scorpions, etc.). The Branchiata are aquatic animals, which breathe 

 through branchiae, or gills, or sometimes through the whole surface of 

 the body. There is but one class under this division, the Crustacea, 

 including crabs, lobsters, shrimps, etc. The common sow-bug is a land 

 form of this branch. 



Having now reached our subject, and traced the insect group dowai 

 to its proper place, we will proceed to deal with this class by itself. 

 The following diagram will present to the reader the position of the 

 class Insecta in its relation with creation: 



( ^Mineral. 



I 

 NATURAL KINGDOM, i Vegetable. 



f Vertebrata. 



I Animal. 



Invertebrata. 



Protozoa. 



Poriferata. 



Coelenterata. 

 I Echinoderiiiata. 



Vermes. 



Arthropoda. 



Molluscoidea. 

 [ ^lollusca. 



The branch Arthropoda may be presented in tabular form, as fol- 

 lows: 



f Tracheata f Class 1. Insecta. 



(Breathing by trachese) i' Class 2. Myriapoda. 



ARTHROPODA -i , i Class 3. Arachnida. 



I Branchi.\ta r 



I (Breathing by branchiae) ■; Class 4. Crustacea. 



I 



Conspicuous examples of the Crustacea are lobsters, crawfish, crabs, 

 shrimps, etc., while the terrestrial forms are represented by the sow- 

 bugs, which are so common in damp locations, and which are frequently 

 mistaken by young entomologists for members of the Myriapoda. 



Class 1, Insecta, is the only one with which we have any immediate 

 concern, although it is necessary to understand something of the other 

 air-breathing classes, which are so nearly related to the insects, and 



