800 MODERN CLASSIFICATION OF INSECTS. 
its cell subsequently to arriving at the perfect state, but was waiting 
for the arrival of spring weather), the abdomen of which exhibited 
at that time the heads of three Stylops larve ; on scaling off one of 
which, a living specimen of the imago of Stylops Spencii (Frontisp. 
Vol. I. fig. 6.) was disclosed; the two other specimens were still in 
the larva state: hence, as the cell of the Andrena is closed by the 
parent at the period of the deposition of the egg with a mass of pollen 
paste, it would appear that the parent Stylops must make its way into 
the cell before it is closed.* The cells of Polistes gallica (ante, p. 239. 
Jig. 19.) (a species infested by Xenos vesparum) are not closed 
until the larva of that wasp is ready to assume the pupa state; and 
hence Professor Peck considered that the Xenos deposited its eggs in 
the larva of the Polistes (Linn. Trans. vol. ii. p. 92.). Mr. Kirby, how- 
ever (Joc. cit.), reasoning from analogy, doubts whether the egg is 
laid in the wasp in its first state, and the larva feeds upon it in its das¢. 
Rossi, however, was of this opinion, since he says of X. vesparum, 
« Cui vespe larva antequam cellule clauderentur forte incunabula 
dedisse videtur.” These circumstances are of considerable interest 
as regards the natural history of these insects, since we are unac- 
guainted not only with the distinctions of the sexes, but also with the 
situation in which the eggs or larvee are deposited, and at what period, 
or in what manner, the connexion between these Hymenoptera and 
their parasites commences. Reasoning from analogy, we might sup- 
pose that in the case of the Andrena, the Stylops has the same instinct 
as the Chrysidide, or other cuckoo-like Hymenopterous parasites, 
which lay their eggs in the nests of Hymenoptera formed in sand or 
wood, and which are similarly closed as soon as the egg and supply of 
food are deposited, and of course before the larva of the fosterer is 
hatched. The larve of these Hymenopterous parasites are, it is true, 
external feeders, but it is not difficult to suppose that the Stylops 
larve, if hatched after the bee larvae, may, as soon as hatched, eat 
into the body of the latter, or even into the pupa. The eggs of 
Xenos may, on the other hand, be at once introduced into the body of 
* G. H. K. Thwaites, Esq., reared many specimens of a Stylops (one of which 
he kindly presented to me), chiefly from females of a species of Andrena, at the 
beginning of May 1838. The male bees, he observed (in a letter to me), do not appear 
till the third week in May ; and at the beginning of June he again observed the 
females of the same bee, but not one of these was infested, so that the stylopized 
bees are at least a month earlier than the others; hence he questions whether 
the short-lived Stylops can lay its eggs in the cells of the latter bees. 
