ithin the body of the
mother-larva; ultimately these abnormally reared young break their way
out. In this case therefore there may be a series of larval generations,
neither pupa nor imago being formed. Extended observations on the
precocious reproductive processes of these midges have lately been
published by W. Kahle (1908). A less extreme instance of an abbreviated
life-story was made known by O. Grimm (1870) who saw pupae of
Harlequin-midges (Chironomus) lay unfertilised eggs, which developed
into larvae. Here the imaginal stage only is omitted from the
life-history. Not always however is it the imaginal stage of the
life-history which is shortened. Reference (p. 18) has already been made
to the case of the virgin female aphids, whose eggs develop within the
mother's body, so that active, formed young are brought forth. Among the
Diptera it is not unusual to find similar cases, the female fly giving
birth to young maggots instead of laying eggs. Such is the habit of the
great flesh-fly (Sarcophaga), of some allied genera (Tachina, etc.)
whose larvae live as parasites on other insects, and occasionally of the
Sheep Bot-fly (Oestrus). In such cases we recognise the beginning of a
shortened larval period, and Brace's investigations in 1895, summarised
by E.E. Austen (1911), have shown that females of the dreaded African
Tsetse flies (Glossinia) bring forth nearly mature larvae, which pupate
soon after birth. In another group of Diptera, the blood-sucking
parasites of the Hippoboscidae and allied families, the whole larval
development is passed through within the mother's body, and a full-grown
larva is born the cuticle of which hardens and darkens immediately to
form a puparium; hence these flies are often called, though incorrectly,
Pupipara. Still more astonishing is the mode of reproduction in the
allied family of the Termitoxeniidae, curious, degraded, wingless
'guests' of the termites, or 'white ants,' lately made known through the
researches of E. Wasmann (1901). Here the individual is hermaphrodite--a
most exceptional condition among insects--and lays a large egg, whence
is usually hatched a fully-developed adult! Here then we find that all
the early stages, usual in the higher insects, are omitted from the
life-story.

Interesting comparison may be made between the total duration of various
insect life-stories. To some extent at least, the length of an insect's
life is correlated with its size, its food, the se