SOME REPRESENTATIV-E INSECTS 377 



these features the arthropods clearly resemble annulates. On the 

 other hand, the existence in arthropods of a hsemocoele instead 

 of a clearly recognizable ccelome is in marked contrast with the 

 condition that is so typical of the annulates. In correlation with 

 this condition is the free communication between the blood vessels 

 and the cavities of the hsemocoele, but the ostia of the arthropod 

 heart are a unique feature of the phylum. 



Some Representative Insects 



Orthoptera. — Among Orthoptera, the crickets and katydids 

 (Fig. 191) resemble the grasshoppers sufficiently in their general 

 external features to be recognized as allied forms. The crickets 

 that are most famihar are the house and field crickets of the genus 

 Gryllus. The antennae are long and slender in correlation with 

 the nocturnal habits of these in.sects, and the hind legs are elongated 

 for leaping as in the grasshopper. The posterior pair of wings is 

 well developed, and the anterior pair specialized as wing-covers, 

 but in many species the wings are reduced in size, and some 

 crickets are wingless. In the males, certain veins of the wings are 

 modified as the sound-producing organs (Fig. 184, p. 365). The 

 " mole " cricket is a type having its anterior legs adapted for 

 burrowing, like those of a mole. The katydids are fike green grass- 

 hoppers with long antenna?. Their " Katy did, Katy did, she 

 did, she didn't " is a famihar sound in the evenings of late summer, 

 for, like the crickets, the katydids are nocturnal in their habits. 

 The life cycles of the crickets and katydids are similar to those of 

 the grasshoppers. IMost species have sword-like ovipositors by 

 which they slit the stems of plants in which their eggs are laid. 



Ephemerida, Plecoptera, Odonata and Tricoptera. — The may- 

 flies, stone-flies, dragon-flies, and caddis-flies, which are represen- 

 tative of their respective orders, may be mentioned together 

 because of the similarity in their hfe cycles. With a few excep- 

 tions, the eggs are laid and the larval stages occur in water. 

 At the final molting the insect comes to the surface and casts 

 its skin for the last time, emerging as the fully developed adult 

 insect. In the may-flies (Fig. 193) the larva can be recog- 

 nized by the three long caudal appendages and gills upon the 

 abdomen. After many molts and at least a fuU year of larval 

 hfe, the adult stage is reached. This lasts but a few hours in 



