xi PHYLUM ARTHROPODA 571 



capable of being grouped in the same orders as the living repre- 

 sentatives of the class, and are looked upon as constituting at 

 least two orders, the members of which are all extinct. 



CLASS IV. INSECTA. 



The class of Insects, comprising the Cockroaches, Grass-hoppers, 

 Dragon-flies, House-flies, Butterflies, Beetles, and Bees, with their 

 many allies, though it is a very extensive one, including as it does 

 a larger number of species than any of the other classes of the 

 Arthropoda, is yet characterised by a remarkable degree of uni- 

 formity, no such extremes of modification occurring as are 

 observable within the class Crustacea. 



Characteristic of all the members of the class is the presence of 

 three clearly-defined regions the head, thorax, and abdomen. 

 There are present on the head, antennae, mandibles, and two pairs 

 of maxillae, the jaws being variously modified in the different 

 orders. All Insects have three pairs of thoracic legs, and most 

 have either one or two pairs of wings likewise borne on the thorax ; 

 the abdomen is not provided with paired appendages. 



The organs of respiration are tracheae similar to those of the 

 M vriapoda. 



The various systems of internal organs attain in all the higher 

 groups of Insects a very high grade of development. In most the 

 development is complicated by the occurrence of a strongly-marked 

 metamorphosis. Insects are terrestrial or aerial, only a few groups 

 living on the surface of fresh or salt water; but many are aquatic 

 throughout their larval condition. 



Many groups of Insects are remarkable for the high grade of 

 their -intelligence as compared with the members of most classes of 

 the animal kingdom. This manifests itself mainly in a number 

 of instincts, often of a remarkable character, having to do with the 

 protection and rearing of the young in some cases leading to the 

 formation of communities consisting of individuals of various 

 different kinds (workers, soldiers, sexual individuals) for mutual 

 support and protection. 



K Ex AMPLE OF THE CLASS THK COCKROACH (Periplaneta 

 (tmericana). 



he Cockroach, familiarly known by the misleading title of 

 lack Beetle," is a common pest of kitchens, bakeries, and store- 

 rooms. It is nocturnal in its habits, rarely coming out of its 

 lurking-places in the day-time, and is almost nu^JBtt-ous in its 

 diet. It is a good example of the Insecta, not only <fl ; ount of its 

 large size rendering it convenient for dissection, bSBso because 



