108 ARTHROPOD A. 



or cuckoo-spit (Ptyelus spumarius), the water boatman (Notonecta 

 glauca}, the bug (Cimex lectularius), and the louse (Pediculus 

 humanus). The latter, a very abnormal form, cannot well be 

 separated from the bird-lice (Mallophaga). The number of spe- 

 cies in this order cannot be estimated at less than 20,000. 



There are five well-marked suborders : the first two are often 

 regarded as forming a distinct order under the name of " Homo- 

 ptera," while the fourth forms the order " Thysanoptera " of 

 Halliday and Westwood. Mallophaga are not regarded as true 

 insects by the latter ; they form the first two of the sixteen fami- 

 lies of Neuroptera according to Von Hayek. 



Potyctenes, a very remarkable form originally described by 

 Giglioli, and which Westwood considers to have an affinity with 

 the Hemiptera, is now approximated by C. Waterhouse to the 

 Pupipara. It is a parasite on bats ; one of its species is from 

 China, the other from Jamaica. 



Thorax normal (of three pieces). 

 Mouth suctorial : without palpi. 

 Wings membranous. 



Tarsi one- or two-jointed PHYTOPHTHIRIA. 



Tarsi three-jointed HOMOPTEKA. 



Anterior wings coriaceous at the base . HETEIIOPTERA. 

 Mouth submandibulate : with palpi THYSANOPTERA. 



Thorax abnormal (of two pieces, or three in- 

 distinct) MALLOPHAGA. 



PHYTOPHTHIRIA ( = Stenorhynchi). Tarsi one- or two-jointed. 

 Antennas of more than six joints. Wings two or four, often 

 wanting. 



The pupae in many cases are not to be distinguished from the 

 imago. The larva, especially in the Aphides, is often covered by 

 a cottony secretion. 



Aphides are mostly viviparous in summer, but oviparous in 

 winter ; in the former case the females are winged. Partheno- 

 genesis goes on among them through many generations. Whole 

 generations are sometimes resident in gall-like excrescences caused 

 by them. A peculiar secretion (honey-dew) is voided from the 

 anal siphunculi of many species. Phylloxera vastatrix is the 

 vine-pest. 



Coccidee have only one-jointed tarsi, the male two-winged, the 

 female apterous. 



