INSECTS. 275 



We see therefore in the perfect Insect the manly period of their 

 tife : in the larva the childish period. Between the two nature has 

 nterposed a deep sleep of development. The marriageable period 

 a deadly for many. There are also many difficulties to be over- 

 liome 1 . Some organs must for a time stand still, others (as for 

 instance, the silk-secreting tubes of caterpillars) must entirely 

 jlisappear. The development of the sexual organs is essential, 

 [tnd for that everything must wait awhile ; these remain during the 

 tarval 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 

 rue object of the phenomena, of which the metamorphosis is 



mposed, which is not so entirely unique in its kind, as might be 

 first supposed. The perfect Insect lives for propagation, and 



icn it has attained that purpose of its_being, it dies to make 



om for others, and serves for food to birds and other animals, 

 s also an annual plant ceases to grow as soon as its bloom is 



veloped, and dies when the seed is come to maturity 2 . 



1 Every casting of the skin is connected with more or less of danger; the moulting 

 also a distressing season for birds ; but especially the last shedding, when caterpillars 



changed into pupae, is frequently fatal. Sometimes the casting is incomplete ; the 

 ad of the caterpillar remains attached to the pupa. In this way may be explained 



occasional occurrence of butterflies with caterpillars' heads. See 0. F. MUELLER, 

 exemption d'un papitton a iite de Chenille, Mem. presentes a I'Acad. des Sc. de Paris, 

 74, vi. pp. 508, &c., Naturforscher, xvi. 1787, s. 203 212, Tab. iv. f. I, 2 ; WES- 

 IEL, Ann. des Sc. not. sec. SeVie. Tom. vm. 1837, Zoologie, pp. 191, 192; BRUINSMA, 

 itengewone afivijlcingen, ^vaargenomen Mj de gedaanteverwisseling des zijdeworms, 

 jdschr., voor natuurl. GescJi. en Physiol. vn. 1840, pp. 257 270, PI. iv. and my 

 a/nteeTceningen thereon, ibid. pp. 271 275. Somewhat different are other observations 



MAJOLI in Boiribyx mori, in which the moths, without having first become pupae, 

 pear to have proceeded immediately from the caterpillars. MECKEL'S Archiv fur die 

 hysiol. II. 1816, s. 542. 



a What is said here relates especially to the complete metamorphosis ; in the 

 complete the changes are less important. Comp. on this subject RENGGER'S Physiol. 

 nters. s. 49 87, and HEROLD'S Entwickelungsgeschichte der Schmetterlinge, Casel 



Marburg, 1815, 4to, (one of the most excellent works on Natural History which 

 ,ve been published in this century), in the numerous plates of which the development 

 ly be followed without a break in the whole and in all its steps. Comp. further, on 

 e changes which the intestinal canal undergoes on metamorphosis, DUTROCHET, 

 urnal de Physique, Tom. LXXXVI. 1818, p. 130, &c., and in MECKEL, Archiv f. d. 

 hysiol. IV. Bd. 1818, s. 285293; and on the changes in the nervous system, NEW- 

 >RT, Philos. Trans. 1832, ji. pp. 383 398, PI. XII. xin. 



182 



