Sept. 1, 1867.] 



IIARDWICKE'S SCIENCE-GOSSIP. 



20." 



one of these is nothing but the Periphyllus men- 

 tioned at the commencement of this note as having 

 been described by the authors who had observed it 

 as a separate genus in the family of the Aphides. 



" Such is, in summary, the singular observation 

 that we have made upon Aphis aceris. We may 

 now give some fuller details upon each of the two 

 kinds of individuals of which this species is com- 

 posed. 



"When we examine with the naked eye or with 

 a lens the embryos of the brown Aphis of the maple 

 at the moment of their being produced by the 

 females, or after opening the bodies of the latter, 

 we see at once that all of them have not the same 

 coloration. In some they are of a tolerably bright 

 green, whilst in others their colour is more or less 

 brownish or greenish-brown. The brown embryos 

 present no peculiarities, and only differ from their 

 mothers by characters analogous to those which are 

 remarked in all species of Aphides between the 

 newly bom young individuals and the adult females. 

 As in these latter, their bodies and appendages are 

 furnished with rather long simple hairs, and, like 

 all young Aphides at the moment of their birth, 

 they already contain rudiments of embryos in the 

 interior of their generative apparatus. If, on the 

 other hand, we examine the green embryos, we at 

 once detect, besides their peculiar coloration, very 

 marked differences between them and their brown 

 congeners. The various parts of the body and limbs 

 do not present the same conformation as in the 

 latter, but one is especially struck by the extraordi- 

 nary development and the unusual appearance of 

 their tegumentary system. Thus their surface is no 

 longer furnished only with simple hairs, but also 

 and principally with scaly transparent lamella), more 

 or less rounded or oblong, and traversed by diver- 

 gent and ramified nervures. These lamella? occupy 

 especially the anterior margin of the head, the first 

 joint of the antenna? (which is very stout and pro- 

 tuberant), the outer edge of the tibia; of the two 

 anterior pairs of legs, and the lateral and posterior 

 margins of the abdomen. Moreover the whole 

 dorsal surface of the latter and of the last thoracic 

 segment is covered with a design having the aspect 

 of a mosaic composed of hexagonal compartments, 

 and which, is not without analogy to the pattern 

 formed bythe scaly platcsof the carapace of tortoises. 

 These peculiarities give our insect a great elegance 

 of appearance, which causes it to be much in re- 

 quest with the amateurs of the microscope in 

 England, where it is commonly known under the 

 name of the 'Leaf-insect.' The entire animal is 

 strongly flattened, and resembles a small scale ap- 

 plied to the surface of the leaf upon which it reposes, 

 and on which it requires a certain amount of care 

 to detect it. 



" Another remarkable character of these abnor- 

 mal individuals of Aphis aceris is the rudimentary 



statc of their generative apparatus. This is reduced 

 'to a few groups of small pale and scarcely visible 

 cells, none of which arrives at maturity to become 

 transformed into an embryo ; and it retains this 

 character as long as it is possible to observe the 

 animal. The functions of nutrition, also, are per- 

 formed in them in a very unenergetic manner ; for 

 from the moment of their birth until that at which 

 we cease to observe them, they increase but little 

 in size, attaining scarcely one millimetre. They 

 undergo no change of skin, never acquire wings like 

 the reproductive individuals, and their antennae 

 always retain the five joints which they present in 

 all young Aphides before the first moult. Never- 

 theless they possess a well-developed rostrum aud 

 an intestinal canal, the peristaltic contractions of 

 which we have distinctly observed. In short, 

 although we have observed them for several months 

 (that is to say, from May to November), no change 

 in their condition was ascertained ; and they dis- 

 appeared with the leaves which bear them, without 

 its being possible to ascertain what becomes of 

 them subsequently. 



"The question naturally arose, What was the 

 signification of these abnormal individuals of the 

 Aphis of the maple, and what part did they fulfil in 

 the reproductive functions of the species to which 

 they belong ? They are evidently not males, since 

 their generative apparatus retains the same rudi- 

 mentary form at whatever epoch we examine them. 

 Moreover in no known species of Aphis are the 

 males produced at the same time as the viviparous 

 individuals, which are not the true females of the 

 species. There is therefore no other alternative 

 but to regard them as a modification of the specific 

 type constantly reproduced with the same characters 

 by the successive normal generations. Our ab- 

 normal Aphides are indeed deprived of the faculty 

 of reproduction, either by sexual generation or in 

 any other manner; but after the observations of 

 M. H. Landois upon the law of sexual development 

 in insects, we know that in them the sexes depend 

 simply upon the conditions of alimentation of the 

 larva. Because, in the present state of things, these 

 conditions have not yet occurred for one of the two 

 sorts of larvae of Aphis aceris, there is no reason for 

 our concluding that they may not some day be 

 realized ; and by thus acquiring, with the attributes 

 of the sexes, the faculty of propagating directly in an 

 indefinite manner, these abnormal individuals will 

 become in their turn the origin of a new species pro- 

 duced by deviation from an anterior specific type." 



Contrary to Nature. — The truth is that folks' 

 fancy that such and such things cannot be, simply 

 because they have not seen them, is worth no more 

 than a savage's fancy that there cannot be such a 

 thing as a locomotive, because he never saw oue 

 running wild in the forest. — Water Bulks. 



