280 MR. F. BALFOUR-BROWNE ON THE [ Mar. 2, 
the earlier stages, and it is possible that a large number of 
nymphs kept under uniform conditions might have caused the 
correspondence to have continued through every stage. 
The correspondence between certain stages in development 
and certain moults has been observed in the larve of other 
insects. For instance, Acrydians moult five times, the wings 
appearing after the second moult and i increasing quite definitely 
at each succeeding moult, the merease in the “last stage being 
very great. “ Besides the acquisition of wings there are slight 
differences at each moult both im structure and colour, besides 
size, so that we may always recognise the comparative age and 
the particular stage of growth of any individual” (Packard, bt: 
9. 595). Tord Av bury (J. ¢. p. 62) noticed that the nymph of 
Chloéon “ oradually attains its perfect condition through a series 
of more than 20 moultings, each accompanied by a slight change 
of form,” and there are numerous other cases cited in works on 
entomology, but, by many authors, no notice seems to have been 
taken of these facts in discussing the question of the significance 
of the moult. 
On this latter point various suggestions have been made, of 
which the simplest, and perhaps the oldest, is that the moults are 
necessary to enable the larva to grow. It is obvious that where 
a larva is encased in a hard intesument, one of two processes is 
necessary in order that the contained organism may Increase in 
size. Hither the integument must be capable of expanding with 
the organism, or it must be cast off from time to time. 
When the nymph moults it expands greatly in size as it creeps 
out of its old skin, and, a few minutes after escaping, is much 
larger than the agin from which it emerged. The nymph has 
therefore been in a state of compression within its skin previous to 
the moult. But growth does not only take place at the moment 
of the moult—for instance, a nymph measuring 1] mm. at the 
commencement of its final stage was 15°2 mim. at the end of it, 
so that the nymph-skin is undoubtedly capable of expansion. 
On the other hand, Dr. Sharp (1895, p. 163) considers that 
growth is only of secondary importance in accounting for the 
moult, urging as one reason that ‘“‘many insects make their first 
ecdysis almost immediately after they leave the egg”; and he 
quotes the case of the blowfly larva, which, “ according to Lowne, 
moults within two hours of its emergence from the egg.” The 
case of the dragonfly pronymph is even more apt in this connection: 
Hisig (1887, p. 781) suggested that the moult was for the 
purpose of getting rid of w aste nitrogenous matter, and Dr. Sharp 
(U. ¢. p. 163) adds that it may be of importance in separating the 
carbonaceous products from the blood. Bataillon (1892, p. 61; 
1893, p. 18) has stated that at the period of the moult the larva 
is inastate of asphyxiation ; and Dr. Sharp (/.c. p. 131), referring 
to this observation, remarked that if it is a fact, ‘‘ the secretion 
of the new coat of chitin may figure as an act of excretion of 
considerable importance.” 
The method of passing to the integument certain waste 
