42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



elaborated by Heslop-Harrison (1958), contends that the larva is a 

 free-living stage of the embryo, and that the pupa represents the 

 condensed nymphal instars of insects without metamorphosis. The 

 idea of embryos climbing trees, eating leaves with fully developed 

 mouth parts, and spinning cocoons, however, sounds like something 

 from science fiction, and the condensation of several active instars 

 into a single immobile stage having no resemblance to a nymph is 

 biologically hard to visualize. Particularly it would seem strange that 

 a flightless "nymphal" stage of a lepidopteron should have adult mouth 

 parts, and the same might be said of other insects having specialized 

 feeding organs in the adult stage, which appear first in the pupa. 



There is nothing inherently improbable about the occurrence of an 

 adult moult between the pupa and the imago ; adult moulting occurs in 

 other arthropods, in the apterygote insects, and the mayflies. Experi- 

 mentally, moulting can be induced in the adult insect as well as in the 

 nymph and larva (see Wigglesworth, 1954, p. 48). The corpus allatum 

 hormone governs both nymphs and larvae alike, and at the end of the 

 juvenile period it gives way to the prothoracic-gland hormone, which 

 produces a moult followed by either an imago or a pupa according to 

 whether the insect is hemimetabolous or holometabolous. These glands 

 in insects without a pupal stage degenerate at the moult to the adult, 

 but in holometabolous insects they persist into the pupal stage. Boden- 

 stein (1953) has shown that even in the cockroach the prothoracic 

 glands do not degenerate at the moult to the adult if the corpora allata 

 are removed without injury to the corpora cardiaca. The young adult 

 cockroach then moults again. In the holometabolous pupa, therefore, 

 when the corpora allata have ceased to be functional, the moult to the 

 imago can be an adult moult effected by the thoracic-gland secretion. 



LIFE OF THE ADULT 



The moth or butterfly is fully formed within the pupal shell and 

 then emerges as a mature insect, except that the internal organs of 

 reproduction may not yet be fully functional. The adult escapes 

 through a slit along the back of the pupa (fig. 16 E). The butterflies 

 have an easy time of getting out, since they are immediately free on 

 emergence. Among the moths, however, many species on emergence 

 from the pupa find themselves still enclosed in a cocoon. Some are 

 fortunate in that the pupa itself has protruded its front end from 

 the cocoon and thus allows the moth to escape. The pupae of Erio- 

 craniidae have large active mandibles by which they tear open the 

 cocoon and come to the surface of the ground where the adult can 



