INSECTA 409 



Collembola have a wide distribution. They are found along the 

 sea shore between tidemarks and submerged by each tide, e.g. 

 Aniirida maritima. Common aquatic forms are denizens of fresh 

 waters, e.g. Podura aquatica. They have been reported to be so 

 abundant in Arctic zones as almost to cover the snow, and in 

 Europe sometimes to be present in such large numbers that the 

 progress of railway trains is impeded owing to their having pre- 

 vented the wheels from gripping the rails. 



Order PROTURA 



Minute insects without wings, eyes or antennae; with piercing mouth 

 parts deeply inserted in the head capsule; with abdomen of twelve 

 segments, the first three of which bear papillae. 



This is a small group of doubtful affinities. Its members are found 

 in decaying organic matter. The fact that on hatching the abdomen 

 is 9-segmented and that subsequent moults bring about the full 

 number of segments is regarded by some authorities as sufficient 

 ground for their inclusion in a class distinct from the Insecta. An 

 example is Acerentomum doderoi of Europe. 



Class PTERYGOTA 



Subclass EXOPTERYGOTA 



Order ORTHOPTERA 



Insects with generalized biting mouth parts ; ligula 4-lobed, consisting 

 of inner paired glossae and outer paraglossae; fore wings rather 

 narrow and somewhat hardened {tegmina) ; hind wings membranous ; 

 abdomen usually with jointed cerci of short or moderate length; 

 ovipositor generally present. 



This order comprises terrestrial insects of large size which have 

 great powers of running and jumping. There are many flightless 

 species in all the families (cf. the female of Blatta orientalis). 



The main structural features are exemplified by Periplaneta, the 

 cockroach. Its generalized character is shown by the character of 

 the mouth parts, the nervous system (six abdominal ganglia), the 

 circulatory system (heart with thirteen chambers, three in the thorax 

 and ten in the abdomen), and the obvious ten segments of the 

 abdomen. 



The order is divided into the Ciirsoria in which the legs are of 

 approximately equal size and the Saltatoria in which the last pair of 

 legs are modified for jumping (Fig. 305). The former consists of 

 the Blattidae (cockroaches) which are swift-running, omnivorous 

 forms, usually tropical in their distribution, the Mantidae (praying 



