4.92 MODERN CLASSIFICATION OF INSECTS. 
nished with short antennz and oral appendages*, the precise structure 
of which has not been described (blind according to De Geer, but 
with two eyes according to Rosel). These larve are very active, 
twisting about in all directions, and feeding upon the fleshy particles 
of feathers and the blood of animals, especially drops of congealed 
blood found lying near the eggs: the last, at least, is stated to be 
their food by M. Defrance+, but this part of the history of the flea 
seems to require elucidation. When full grown, which occurs, in 
summer, in about twelve days, the larve enclose themselves in a 
small cocoon of silk, often covered with dust, and attached to ad- 
joining substances. Rosel, however, observed that some of the larvee 
underwent their transformations without forming any cocoon. The 
pupa (jig. 123. 16., 14. ditto magnified, 15. exuvia of the larva) is 
quite inactive, with the legs enclosed in separate cases; the colour of 
the pupa is at first dirty white, but it afterwards assumes the tint of 
the imago. The larve, which are not hatched until the end of the 
summer, pass the winter in that form. The period cf the duration 
of the pupa state varies from eleven to sixteen days. 
The changes which the flea undergoes were not unknown to Aris- 
totle, since he noticed not only that it had distinct sexes, but also 
that they produced oxwAne woeweic: from not, however, tracing the 
insect through its changes, he fancied this progeny was swt generis, 
and that the perfect insect was generated spontaneously in the earth, 
the Latin name Pulex being stated by Isidorus to have been derived 
from pulvis, “ quasi pulveris filius.” Mouffett also entertained a 
similar notion, whilst Scaliger thought they were produced from the 
humours amongst the hairs of dogs. It is to Leuwenhoeck (Arcana 
Nature, tom. i. p. 35. and 353.), Rosel (dns. Belust. tom. ii., Muse. et 
Culie. tab. 2, 3, 4.), and De Geer (Mémoires, tom. vii. tab. 1.), that we 
are indebted for a knowledge of the real transformations of the insect. 
There are numerous species of this genus, peculiar to various 
animals and birds. Duges describes four species, P. irritans, Canis, 
Musculi, and Vespertilionis ; whilst Bouché describes ten species, P. 
irritans, Canis, Gallincee Schr., Felis, Martis, Sciurorum, Erinacei, 
* The precise structure of these mouth organs has not been described: hence we 
are in doubt as to whether the larva be suctorial or mandibulated ; if the former, the 
analogy of the order with the Coleoptera cannot be maintained. 
+ In the chapter on the flea, in the Natural History of Insects, in the Family 
Library, vol. ii., I have given an abstract of M. Defrance’s obseryations, which 
are also stated in the Hncycl. Méth. tom.x. p. 242. 
