XII] OKDERS OF INSECTS 253 



avoided. Wings are only developed on the sexually ripe Insects at 

 the time when they swarm out from the nests and when cross 

 fertilisation can take place. Isoptera are confined to the tropics 

 and are fearfully destructive of furniture, clothing, etc. Two forms, 

 Caktermes and Eutermes come as far north as Sicily. 



Order VI. Thysanoptera, or Corn-flies. 



These are minute black Insects which infest flowers including 

 under that title the inflorescences of corn and other grasses. The 

 wings are fringed with hairs The basal parts of the maxillae 

 coalesce to form a tube. One mandible only is developed and this 

 forms a curved stylet. The nymph resembles the adult except in 

 possessing no wings, but a motionless pupal stage intervenes 

 between larvae and adult forms Thrips is the common British 

 genus. 



Order VII. Trichoptera, or Caddis-flies. 



In these Insects a sucking tube is formed by the coalescence of 

 both pairs of maxillae and the mandibles are vestigial or entirely 

 absent in the imago, so that as -in Lepidoptera nutrition has to be 

 obtained from such sources as honey, in which a preliminary stabbing 

 of the host-plant is not required. The wings are covered with 

 hairs, which may be compared to the scales on the Lepidopteran 

 wing, since these latter are only flattened hairs. The larva resembles 

 the larva of Ephemeroptera: it has biting mouth-parts and tracheal 

 gills attached to the abdomen and is aquatic in habit. It constructs 

 for itself a case of bits of stone or shell which ensheaths and pro- 

 tects the abdomen and which when larval life is over serves as a 

 case to protect the pupal or motionless stage which intervenes 

 between the larval and imaginal stages. Phryganea is a British 

 example of this order. 



Order VIII. Neuroptera (sensu stricto). 



These Insects possess biting mouth-parts. The larvae are some- 

 times terrestrial and sometimes aquatic and in the latter case they 

 possess tracheal gills which like those of Day-fly nymph are modified 

 abdominal legs. The wings of the adult are devoid of hairs. There 



