VIII PSVLLIDAE APHIDAE 58 I 



parts, of a leaf, giving rise either to crumpling or to growth of a 

 portion in one direction only, so that on one surface of the leaf 

 a swelling is formed, and on the opposite side a more or less deep 

 cavity in which the Insect dwells. A formation of this kind on 

 the leaves of Aegoiwdium jiodagraria is described by Thomas ^ who 

 states that the growth is due to the deposition of an egg of the 

 Psylla, and is independent of the after life of the Insect ; a fungus 

 — Fuccinia aegoj^odii — forms similar structures on the leaves. 

 Structures much more definite than this may be the result of the 

 attacks of Psyllidae ; for an example the reader may refer to 

 Eeaumur's account of Psylla luxi? In Australia and Tasmania 

 there are Psyllidae known as Laap or Lerp Insects, the products 

 of which are called leaf-manna or Lerp, and are used as food. 

 This manna is a scale produced by the young Insect on the leaves 

 of Eucalyptus as a covering or protection. The scale is 

 fastened to the leaf by a hinge, and is somewhat like the shell 

 of a cockle. Although the scales are said to be in some cases 

 objects of great beauty, very little is known about these Australian 

 Psyllidae, one of which has, however, been referred by Schwarz 

 to the genus Spondyliaspis, Signoret.^ About 160 species of 

 Psyllidae are known to occur in the Palaearctic region, and about 

 fifty of them have been found in Britain.^ 



Fam. 7. Aphidae {Plant-lice or Green-fiy.) — Minute Insects ; 

 (IS usucdly met toith destitute of ivings, tliough many individuals 

 li.ave two pairs of transparent wings. Antennae long, or moder- 

 ately long, three- to seven-jointed ; ctbdomen freqiiently with a pair 

 of tutes {siphons), or short processes on the upper side of the fifth 

 abdominal segment. Tarsi two-jointed, first joint sometimes 

 excessively short. — These soft-skinned Insects are frequently called 

 lilight, and are so abundant in temperate climates that a garden, 

 however small, is sure to afford abundance of specimens during 

 the warm months of the year. This great abundance is due to 

 peculiarities in the physiological processes that render these 

 obscure little animals highly important- creatures ; the individual 

 life for several generations is restricted to constant, or at any rate 

 copious, imbibition of food, accompanied by an almost uninterrupted 



^ Zeitschr. Naturw. (2) xii. 1875, p. 438. 



- Reaumur, M6m. iii. 1737, Dixieme Memoire. 



* P. ent. soc. Wasliington, iv. 1897, p. 66. 



•* For list see Scott, Ent. Mag. xviii. 1882, p. 253. 



