STATES OF INSECTS. 19l 



jection of it, in which it is stripped off by the animal it- 

 self like a worn shirt, being observable, till you descend in 

 the scale to the Serpent tribe a , which at certain periods 

 disengage themselves from their old integument, and start 

 forth with that new and deadly beauty so finely described 

 by the Mantuan bard : — 



" So from his den, the winter slept away, 



Shoots forth the burnished snake in open day; 



Who, fed with every poison of the plain, 



Sheds his old spoils and shines in youth again : 



Proud of his golden scales rolls tow'ring on, 



And darts his forky tongue h , and glitters in the sun." 



Pitt. 



In these the new skin, I imagine, is formed under the 

 old from the rete mucosurti; but in insects, as I formerly 

 stated c , since the time of Swammerdam it has generally 

 been believed by entomologists, that the larva includes a 

 series of cases or envelopes, one within the other, con- 

 taining in the centre the germe of the future perfect insect, 

 whose development and final exclusion take place only 

 when these cases have been successively cast off. This 

 hypothesis, as was explained to you on a former occasion d , 

 has been controverted by a late writer, Dr. Herold ; who 

 affirms that the skins of caterpillars are also successively 

 produced out of the rete mucosum. I have however, I 

 hope, satisfied you that the old system is most consonant 



a In the human species, after certain fevers a simultaneous and 

 total moult, if the term may be so applied, takes place. I experi- 

 enced this myself in my boyhood; when convalescent from Scarlatina, 

 the skin of my whole body, or nearly so, peeled off. 



b The translator, more ignorant of natural history than his author, 

 has turned the " Unguis micat ore trisulcis " of Virgil, into " darts hi? 

 forky sting." 



c Vol. I. p. 70. d See above, p. 52'—. 



