INSECTS. 29 
We see therefore in the perfect Insect the manly period of their 
life: in the larva the childish period. Between the two nature has 
interposed a deep sleep of development. ‘The marriageable period 
is deadly for many. There are also many difficulties to be over- 
come’, Some organs must for a time stand still, others (as for 
instance, the silk-secreting tubes of caterpillars) must entirely 
disappear. The development of the sexual organs is essential, 
and for that everything must wait awhile; these remain during the 
larval state behind other organs; now they repress in turn by their 
development the activity of other organs. Finally, the perfect 
Insect comes forth, in many respects a new creature. This is the 
true object of the phenomena, of which the metamorphosis is 
composed, which is not so entirely unique in its kind, as might be 
at first supposed. The perfect Insect lives for propagation, and 
when it has attained that purpose of its being, it dies to make 
room for others, and serves for food to birds and other animals. 
Thus also an annual plant ceases to grow as soon as its bloom is 
developed, and dies when the seed is come to maturity”. 
1 Every casting of the skin is connected with more or less of danger; the moulting 
is also a distressing season for birds; but especially the last shedding, when caterpillars 
are changed into pupa, is frequently fatal. Sometimes the casting is incomplete ; the 
head of the caterpillar remains attached to the pupa. In this way may be explained 
the occasional occurrence of butterflies with caterpillars’ heads. See O. F. Murtumr, 
Description @un papillon a téte de Chenille, Mém. présentés & UV Acad. des Se. de Paris, 
1774, VI. pp. 508, &c., Natwrforscher, XVI. 1787, 8s. 203—212, Tab. Iv. f. 1, 2; WuEs- 
MAEL, Ann. des Sc. nat. sec. Série. Tom. vu. 1837, Zoologie, pp. 191, 192; BRUINSMA, 
buitengewone afwijkingen, waargenomen bij de gedaanteverwisseling des zijdeworms, 
Tijdschr., voor natuurl. Gesch. en Physiol. vu. 1840, pp. 257—270, Pl. iv. and my 
Aanteekeningen thereon, ibid. pp. 271—275. Somewhat different are other observations 
of Masout in Bombyx mori, in which the moths, without having first become pupe, 
appear to have proceeded immediately from the caterpillars. MZEcKEL’s Archiv fiir die 
Physiol. 1. 1816, s. 542. 
2 What is said here relates especially to the complete metamorphosis; in the 
incomplete the changes are less important. Comp. on this subject RENGGER’s Physiol. 
Unters. s. 49—87, and HeEroup’s Hntwickelungsgeschichte dev Schmetterlinge, Casel 
u. Marburg, 1815, 4to, (one of the most excellent works on Natural History which 
have been published in this century), in the numerous plates of which the development 
may be followed without a break in the whole and in all its steps. Comp. further, on 
the changes which the intestinal canal undergoes on metamorphosis, DuTRrocHEr, 
Journal de Physique, Tom. LXxxvi. 1818, p. 130, &e., and in MEcKEL, Archiv f. d. 
Physiol. tv. Bd. 1818, s. 285—293; and on the changes in the nervous system, Nrw- 
port, Philos. Trans. 1832, 11. pp. 383—398, Pl. x11. x11, 
18—2 
