328 



LEPIDOPTERA 



CHAP. 



quantity of cream-like matter, including the results of histolysis 

 but this, as well as the condition of the internal organs, differs 

 much according to whether the change from the caterpillar to 

 the moth is much or little advanced. 



Many pupae are protected by cocoons. These are masses of silk 

 very various in form disposed by the caterpillar around itself 

 during the last stage of its existence. Some of these cocoons are 

 so perfect that the moth has considerable difficulty in escaping 

 when the metamorphosis is complete. Various devices are used 

 for the purpose of emergence ; the Puss-moth excretes a corrosive 

 fluid, containing potassium hydroxide, and then protects itself 

 from this by retaining on the head while passing through it a 

 shield formed of a portion of the pupa-skin. 1 Lepidopterous pupae 

 usually have the body terminated by a projection of very various 

 and peculiar form called " cremaster." In certain cases these 

 projections are used for the suspension of the pupa, and are then 

 frequently provided with hooks (Fig. 177, C, D). In other cases 

 the cremaster is frequently called the anal armature (Fig. 205, B). 



The development of the wings 

 of Lepidoptera has recently been 

 much studied. It has been known 

 since the time of Lyoimet, that 

 the rudiments of the wings exist 

 inside the body of the caterpillar 

 when it is nearly adult. Verson 

 considers that he has detected the 

 rudiments in the silk-worm larva 

 even before hatching, and he 

 attributes their origin to a 

 modification of form of those 

 cells that occupy 

 the spiracles 



of the second and third thor- 

 segments might be looked 

 (It will be recollected that 



,c 



acic 



FIG. 168. Wing -rudiments of Pieris hypodei'llial 

 brassicae. A, Rudiments of a wing , , 

 before the first moult of the cater- wl1 



pillar : ce, embryonic cells ; ch, ex- 

 ternal cuticle ; h, hypodermis ; o, 

 opening of the invagination ; tr, 

 trachea. B, posterior wing-rudiment 

 of full - grown caterpillar ; b, semi- 

 circular pad ; c, a bundle of the there are no spiracles on these 



two thoracic segments in Lepi- 

 dopterous larvae). Gonin has 

 examined the wing-rudiments in the caterpillar, a few days old, of 



rolled tracheae ; e, envelope ; i, pedi- 

 cel ; tr, trachea. (After Goniu.) 



1 Latter, Tr. cut. Soc. London, 1895, p. 399. 



