ENTOMOLOGY IX OUTLINE SYSTEM IX NATURE, 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. 



M <.>llv sea 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 tracheaB 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 branchia?, 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 down 

 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 In*ecta in its relation with creation: 



MINERAL. 



j 



NATURAL KINGDOM. ' VEGETABLE 



( VERTEBRATA. 



Protozoa. 



ANIMAL. <J Poriferata. 



Coelenterata. 



T i Echinodermata. 



I INVERTEBRATA. J. _. 



I Vermes. 



Arthropoda. 



Molluscoidea. 



Mollusca. 



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

 lows : 



( TRACHEATA f Class 1. Insecta. 



(Breathing by tracheae) {' Class 2. Myriapoda. 



ARTHROPODA 



I Class 3. Arachnida. 

 BRAXCHIATA r 



(Breathing by branchia?) \ Class 4. Crustacea. 



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, Insect a, 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 nearlv related to the insects, and 



