150 ; Miscellaneous. 
be the starting-point of peculiar races. The following observation 
proves not only that simple races are produced in this manner, but 
that forms described as species, or even as actual genera, sometimes 
acknowledge no other origin. | 
In 1852 an English naturalist, Mr. J. Thornton, indicated, under 
the name of Phyllophorus testudinatus, an Hemipterous insect which 
he had found on the leaves of the common maple (Acer campestre), 
and which he regarded as the larva of an undetermined species of 
Aphis. Subsequently, in 1858, Mr. Lane Clark also observed it, 
and placed it, under the name of Chelymorpha phyllophora, in a 
genus intermediate between the Aphidide and the Coccide. Lastly, 
in 1862, M. van der Hoeven, of Leyden, described it, also as a new 
genus, replacing the generic names Phyllophorus and Chelymorpha 
by that of Pertphyllus, the other names being previously employed 
to designate other genera of insects ; and our Hemipteron received 
from the illustrious Dutch naturalist the name of P. testudo. Like 
Mr. Thornton, M. van der Hoeven regarded it as the larva of an 
Aphis of which the adult form was still unknown. 
These brief historical indications form a summary of all that was 
known about this insect when we on our part undertook some inves- 
tigations upon it, the results of which we now propose to communi- 
cate. We first ascertained that, far from constituting a new genus 
or even a distinct species, the Periphyllus is really nothing but the 
larva of one of the known species of Aphides which live on the maple 
—namely, Aphis aceris, a brown species which is to be met with 
during a great part of the year upon the leaves and at the extremi- 
ties of the young shoots of that tree. But, at the same time that 
we ascertained this fact, we were set on the track of a most unex- 
pected discovery, constituting a new and very remarkable peculiarity 
in the development of the animals of this group, already presenting 
such curious phenomena in connexion with their reproduction. 
This was the faculty, become transmissible to all the generations 
of a particular species, of engendering two kinds of individuals—one 
normal, the other abnormal—of which the former alone, after their 
birth, continue the course of their development, and become capable 
of reproducing the species ; whilst the latter retain throughout their 
existence the form which they possessed on coming into the world, 
and appear to be incapable of propagating. Moreover these two 
categories of individuals present such marked characters that, with- 
out having watched their birth, and being thus convinced that they 
are really produced by identical females, and sometimes even by one 
and the same mother, one would inevitably consider them to belong 
to two species, nay even to two completely different genera. Now 
one of these is nothing but the Periphyllus mentioned 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 composed. 
