Glass 3. Insecta. Order 2. Bhynchota or Hemiptera. 257 



■deposits the eggs in branches of trees by means of an ovipositor; tie larvae, 

 wbose fore legs are adapted for digging, make their way down into the earth, 

 where they feed upon the juices of roots ; they only leave the earth just before 

 metamorphosis, climb into a tree and moult for the last time : the imagines 

 Buck young shoots. This division is confined to warm countries, but there is a 

 single species in England. In Noi-th America the Seventeen-years 

 Cicada {Cicada septendecim) occurs: its development lasts seventeen years (a 

 variety of the same species has a period of development which lasts thii-teen 

 years). 



2. The Prog-hopper (Aphrophora sptimaria) is a small Homopteran, 

 peculiar in that the soft, thin-skhmed larva, which lives on the juices of 

 various plants, surrounds itseK with a foamy secretion (cuckoo spittle). This 

 insect belongs to the family CicadellidBe, of which there are several other 

 species in Britain ; most of them can spring long distances. 



3. The Green-flies {Aphidse) form a large family of the Homoptera, the 

 members of which are characterised by the bidky, thin-skinned body, feeble legs, 

 sparse veining on the wings, and small size ; very often the wings are absent, 

 ■especially from the females ; they ai-e inert animals, living together in colonies. 

 Many of them possess glands for the secretion of delicate wax thi-eads which 

 ■surround the body as a woolly mass; in many, also, there is a pair of glands 

 •opening posteriorly on the dorsal side of the abdomen, by two apertiu'es which are 

 situated either on papillse, or at the top of long projecting tubes ; these glands 

 secrete a fatty substance.* Heterogony usually occui-s ; several virginal genera- 

 tions are followed by a generation of males and females. 



(a) Aphides, Green-flies in a restricted sense of the word, are green or black, 

 soft-bodied Insects, with but little power of movement. They live in large 

 colonies, and are extremely abundant on the leaves of all kinds of herbaceous 

 and woody plants ; they have faii-ly long antenna, and two long tubes on the 

 abdomen. In the course of the summer, several successive generations of 

 females occiu% which possess no seminal pouch, and which reproduce partheno- 

 genetically ; the eggs develop in the oviducts, so that the Insects are viviparous ; 

 some of these females have wings, but the majority are apterous. Finally, in the 

 autumn, there is a generation of usually vpingless females and winged males, 

 which copulate, produce eggs, and die. These eggs give rise to the fh-st female 

 generation the following spring. 



(6) The Vine-louse {Phylloxera vastatrix), famed on account of the 

 terrible devastation it works in vineyards, especially those of Trance ; indigenous 

 to North America, where it does no great harm, it was accidentally introduced 

 into Em'ope a few decades ago -with American vines. The tubes are wanting 

 on the abdomen, and it has shoi-ter legs and antennse than Aphis. In 

 the spring, wingless females appear and feed on the roots, causing knotty 

 ■swellings. Each lays abotit thii'ty or forty unfertilised eggs, from which a 

 generation of individuals like the parent arises. In this way, from five to eight 

 similar generations occur dm-ing the summer. At last, from the eggs of the 

 apterous females, a generation of winged females develops. They leave the roots 

 before metamorphosis (and, therefore, when the ■wings are incipient only), and 

 betake themselves to the shoot part of the vine, where each deposits about four 

 unfertilised eggs. These eggs are of two sizes : from the larger, females hatch 

 out, from the smaller, m al es. Both sexes are small, apterous, -with rudimentary 

 mouth-parts, and no alimentary canal, so that no food can be taken. Af-ter 

 impregnation, each female lays a single egg, which before being deposited. 



* " Honeydew," a sweet sticky fluid, the excreta of the Aphides, occurs upon the 

 plants on which they are living. 



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