614 THE MICROSCOPE. 



what the Eev. J. Thornton stated in 1852, to whom 

 we owe its discovery on the leaves of the maple ; he, 

 believing it to be a species of Aphides, called it Phyl- 

 lopJwrus testudinatus. Subsequently it attracted the 

 attention of the Dutch naturalist Van der Hoeven, 

 who regarded it as the larval form of an undetermined 

 species of Aphis, and named it Periphyllus. It has more 

 recently engaged the attention of Dr. Balbiani and M. 

 Siguoret, whose united investigations are given in the 

 " Comptes Eendus " of June 17, 1867. They have posi- 

 tively ascertained that it is the larva of Aphis aceris ; a 

 brown species is also met with during a great part of the 

 year upon the young shoots of the maple. At the same 

 time a curious fact was made out, constituting a new and 

 remarkable peculiarity in the development of this group 

 of insects, already presenting so many curious phenomena 

 in connexion with their reproduction. It really appears 

 that the female produces two kinds of young one normal, 

 the other abnormal; the first arc alone capable of con- 

 tinuing the course of their development, and capable of 

 reproducing the species ; whilst the latter retain their 

 original form, which is never changed throughout their 

 existence. They increase so little in size, that it appears 

 almost doubtful whether they eat ; the mouth is so very 

 rudimentary that this surmise in some measure gains sup- 

 port from the circumstance ; they undergo no change of 

 skin, never acquire wings like the reproductive insect, 

 and their antennae always retain the five joints which 

 are peculiar to all young Aphides before the first moult. 

 Neither are they all of the same colour, some being of a 

 bright green, as represented in our Plate, while others are 

 of a darker, or brownish-green, colour. The brown-green 

 embryos differ from the adult female only in those cha- 

 racters analogous to all other species ; and that chiefly 

 with regard to the hairs, which are long and simple. In 

 the green embryos, in the place of hairs, the body is sur- 

 rounded with scaly, transparent lamellae, more or less 

 oblong in shape, each of which is traversed by divergent 

 ramifying nervures. These lamellae not only occupy the 

 body, but also the anterior part of the head, the first joint 

 of the antennae, and the outer edge of the tibiae of the 



