APHID JE. 



C 



times thickened ; tarsi two-jointed. The 

 body is sometimes clothed with a mealy or 

 cottony secretion, secreted by roundish 

 warts which stand in rows upon the back ; 

 in some species this covering is so long that 

 the animal is entirely concealed by it, and 

 looks merely like a moving flock of wool. 

 It is sometimes employed by the females as 

 a covering for their eggs. 



The Aphidae, like the rest of the order to 

 which they belong, are active in all their 

 stages ; the pupae being distinguishable from 

 the perfect insects only by their possessing 

 the rudiments of wings upon the back of 

 the thoracic segments. In the wingless 

 species this distinction of course does not 

 exist. 



These insects reside, usually in large 

 societies, upon almost every species of 

 plant ; but the different species of plant- 

 lice, like the true lice of animals (Anoplura), 

 are generally restricted to one or two parti- 

 cular plants ; or when they are common to 

 a greater number of vegetable species, the 

 latter are usually very nearly allied. Each 

 species is also restricted to some particular 

 part of the plant ; but no part is exempted 

 from the attacks of particular species, which 

 are found upon the young shoots, the buds, 

 the leaves, the stem, even of trees, and the 

 roots. Of these parts they suck out the juices, 

 by placing the rostrum in a perpendicular 

 position, and forcing the included bristles 

 into the tissues of the plant ; the wound 

 thus formed is frequently enlarged by move- 

 ments of the body of the animal. In some 

 instances the irritation caused by these 

 wounds, inflicted by a colony of Aphides, 

 gives rise to a distorted state of leaves and 

 twigs, and even to gall-like excrescences, in 

 the interior of which the insects may be 

 found in great numbers. 



The abdominal tubercles or tubes above 

 mentioned, which, however, are reduced to 

 simple openings in some species, are gene- 

 rally regarded as excretory organs, through 

 which a saccharine fluid is exuded. This 

 fluid is produced by many Aphides, especially 

 those which live upon trees and shrubs, in 

 great abundance ; it constitutes the well- 

 known honey-dew, which drops in large 

 quantities from some of our common trees 

 (particularly the Lime), and forms small 

 shining spots upon their leaves. The latter 

 were supposed by Liebig to be products of 

 a disease of the plants upon which they 

 occur. The sweet fluid is much liked by 

 ants and other Hymenopterous insects, 



2 ] APIIID.E. 



which seek the Aphides for the purpose of 

 sucking it from them, sometimes inducing 

 them to excrete it by stroking them with 

 their antennae, but sometimes biting and 

 tearing them to get at it. Kaltenbach con- 

 siders the abdominal tubes to be merely pro- 

 duced stigmata, and states that the saccha- 

 rine fluid is emitted through the anus; this 

 is also the opinion of De Geer, Kyber, and 

 others. 



The propagation of the Aphides presents 

 some most remarkable peculiarities, and is 

 well worthy of a careful study . The ordinary 

 colonies of these insects, which may be met 

 with everywhere during the summer, consist 

 of winged and wingless individuals, the 

 latter being for the most part larvae and pupae. 

 The winged individuals are all viviparous and 

 capable of producing young larvae without 

 any intercourse with a male insect. During 

 the whole course of the summer, none but 

 these so-called viviparous females are to be 

 met with, and generation follows generation 

 without the appearance of a single male. 

 It is only in the autumn that males and true 

 females are produced as the last result of the 

 viviparous reproduction ; the latter are 

 usually apterous, even in the ordinarily 

 winged species ; and, after copulating, the 

 females lay eggs, which serve to continue 

 the race in the following summer. The 

 viviparous individuals of some species are, 

 however, said to live through the winter j 

 and the viviparous reproduction may be con- 

 tinued uninterruptedly for an indefinite 

 period by the maintenance of the necessary 

 conditions of temperature &c. ; at least 

 Kyber observed it for four consecutive 

 years in a colony kept in a room at a uni- 

 form temperature. The males are rarer, 

 mostly alate, and with a smaller abdomen. 



The true nature of this wonderful mode 

 of propagation has been the subject of much 

 dispute, especially of late years. It will be 

 unnecessary for us to enter upon the con- 

 sideration of the various opinions that have 

 been put forward ; it is sufficient to mention 

 that it is now generally admitted to be an 

 example of the alternation of generations or 

 parthenogenesis, which occurs so frequently 

 amongst the lower animals, the viviparous 

 forms being regarded as the products of a 

 sort of internal gemmation. According to 

 Huxley, the organs in which the young of 

 the viviparous forms are produced (pseitdo- 

 varia) are strictly homologous with the true 

 ovaries, and the germs of both forms are 

 identical, (the existence of the germinal spot 



