Glass 3. Insecta. Order 1 . Orthoptera. 



255 



labial palps, but witii a very broad labium. The legs feeble. Abdomen usually 

 elongate witb two unjointed cerci. Extremely good fliers, seizing their prey 

 {e.g. Butterflies) upon the wing.* The larvEe inhabit fresh water, and are- 

 characterised by the modification of the labium into a long eversible prehensile 

 organ (the mask), and further by the closure of all the stigmata ; respii-ation is 

 effected by means of tracheal gills which in some cases are lamellate and situated 

 at the end of the abdomen, whilst in others they are represented by a number of 

 folds developed in the rectum ; in the latter case the rectum receives and ejects 

 water rhythmically. The larvse of the last species move by spirting the water out 

 of the rectum. Here belongs the genus Libellula, in which the hind wings are- 

 broader at the base than at the tip, and the large eyes are pushed together into 

 the middle of the head ; the larva) -with rectal branchiae : also the delicate slim 

 .4jrrio)i-species (Demoiselle flies) in which the hind wings are narrower at their- 

 bases than at the ends, the eyes are -wide apart and the larvse possessed of three 

 external gills. 



9. May-flies (genus Ephemera and others) are usually small insects 

 with four thin wings, of which the hinder are smaller than the anterior. The- 

 mouth-parts of the imago are rudimentary ; the 



abdomen -with three anal filaments posteriorly. The 

 lai-vae live in water, and like the Dragon-flies possess 

 a closed tracheal system and leaf-hke or branched 

 tracheal gills, situated in a row along each side of 

 the abdomen ; they exhibit three thread-like ap- 

 pendages, as does the imago. The larvaa are pre- 

 daceous, and have well- developed mouth-parts ; some 

 of them dig passages in banks. The May-flies pass 

 through a sub-imaginal stage (c/. p. 247) ; as imagines 

 they take no food, and many species live for only a 

 few hours during the night, metamorphosis occurring 

 in the evening ; others a few days ; whilst the larval 

 life, at least in some cases, lasts for two years. 

 Several species common in England. 



10. Book-lice {Troctes), are small apterous 

 Orthoptera, which chiefly occur between old paper, 

 in collections of Insects, and so forth ; together -with 

 their winged relatives (Psocus), which live in forests, 

 they form a special small family -within the order. 



11. To this order also belong the Mallophagidse, 

 small, flat, lice-like animals, -with fairly hard chitiuous 

 exoskeleton ; the head is broader than the prothorax, 

 and carries the usual biting mouth-parts, of which 



the mandibles are specially weU developed. The antennae have from three to five 

 joints, there is one ocellus on each side of the head, but this may be absent- 

 The tarsus consists of one or two joints with one or two claws ; at the lower 

 end of the tibia is a process against which the claws may be bent back 

 the legs are thus adapted to gripping hairs or the barbs of feathers. The 

 numerous species of this division all live upon Mammalia and Birds, gnawing- 

 the epidermis, hairs and feathers. The chief species occmTing on Mammalia 



Fig. 213. 

 (Lepisma). 



Sugar-mite. 



* Copulation is very peculiar among the Dragon-flies. The second abdominal 

 segment of the male is enlarged, and furnished -with a oopulatory apparatus. Before 

 pairing, this is filled with spermatozoa from the vas deferens, which opens at the end 

 of the body. The operation is effected by flexure of the abdomen. The male then 

 seizes the female round the neck by means of the cerci, and the female arches its body 

 so that the abdominal extremity reaches the male copulatory organ, and coitus is 

 effected. 



