1909. | LIFE-HISTORY OF THE AGRIONID DRAGONFLY. 281 
products of the metabolism is almost universal throughout the 
animal kingdom, aud there seems no reason why it should be 
regarded as, in insects, a special process of excretion. Whatever 
may have been the primary cause, the process has apparently been 
seized upon by Natural Selection, which has eliminated the less 
protected individuals, and produced a tough protective exo- 
skeleton. 
Bataillon’s observations do not seem to me as important as 
Dr. Sharp regards them in demonstrating that the moult is a 
special act of excretion. When it is remembered that the larva, 
immediately after a monlt, is soft and helpless, unable to feed, 
and an easy prey to almost any hungry animal, it is possible to 
believe that those individuals which did not quickly produce a 
new protective armour were eliminated in the struggle for 
existence. In order to quickly produce a new hard skin, a larva 
would necessarily retain a large amount of waste products which 
would otherwise pass out of the system, and this might account 
for an asphyxiated condition immediately prior to the moult. 
Pantel (1898) considered the moult as necessary to account 
for the formation of ectodermal organs, and points out that, at 
each of the three stages of the larva of Thrixion, new characters 
appear; while Packard apparently held much the same view, 
as he says (/. c. p. 615), “the swollen bodies of the gravid female 
of Gastrophysa, Meloé, or of Termites and of the honey-ant show 
that the skin can stretch to a great extent, but in the meta- 
morphoses of Crustacea and of Insects, the young of which are 
more or less worm-like or generalised in form, with fewer segments 
and appendages, or with appendages adapted for quite different 
uses from those of mature life, the necessity for a change of skin 
is seen to be necessary for mechanical reasons. Hence Crustacea 
and Insects moult most frequently early in life, when the changes 
of form are most thoroughgoing and radical, while simple growth 
and increase in size are most rapid at the end of the larval life, 
as seen in both shrimps and crabs, and in insects.” 
Now it seems to me that the fact that the larva is in a state of 
compression within the old shell at the time of the moult, 
suggests that the moult is necessary for growth, while the fact 
that certain stages of development are correlated with certain 
moults suggests that the moult is necessary for development, and 
Tam inclined to think that a moult may be either a “‘ growth- 
moult” or a ‘‘ developmental moult,” or a combination of the two. 
Growth and development are, to some extent at least, inde- 
pendent phenomena, since we find variations in size in equally 
mature individuals, and apparently either growth or levelopment 
may be retarded without the other being affected, as any rate to 
the same extent. 
From the fact that certain stages in the life-histery of a larva 
are correlated with certain advances in development, growth 
cannot possibly control the moults producing those stages, and 
they must be primarily ‘developmental moults.” Further, 
Proc. Zoou. Soc.—1909, No. XIX, 19 
