,28 



LEPIDOPTERA 



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

 ■ — hut this, as well as the condition of the internal organs, differs 

 much according to wliether the change from tlie caterpillar to 

 the moth is much or little advanced. 



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

 — -very various in form — disposed hy the caterpillar around itself 

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

 so perfect that the moth lias considerable difficulty in escaping 

 when the metamorphosis is conqdete. Various devices are used 

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

 liuid, containing potassium hydroxide, and then protects itself 

 from this hy retaining on the head while passing through it a, 

 shield formed of a portion of the pupa-skin.^ Lepidopterous pu])ae 

 usually have the body terminated l)y 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, I)). In other cases 

 the cremaster is frequently called the anal armature (Fig. '20'i, !'> ;. 



The development of the wings 

 of Lepidoptera has recently been 

 much studied. It has been known 

 since the time of Lyonnet, that 

 the rudiments of the wings exist 

 inside the body of the caterpillar 

 when it is nearly adult. Yerson 

 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 

 Fio. l68.^Whig-ruiliments of Pieris liypoderuial cells that occupy 



brassicae. A, Rudiments of a wiug , , , , , , . , 



before the first moult of the cater- the spots where the spiracles 



pillar: ce, embryonic cells ; ch, ex- of the Secoud and third thor- 

 ternal cuticle ; h, hypodermis ; o, . • i j. i ^ ^ ^ 



opening of the invagination; ir, ^^cic Segments might be looked 



trachea. B. posterior wing-rudiment fop. (It will be rCCOllectcd that 

 of full-grown caterpillar; h, semi- • i i 



circular pad: c, a bundle of the there are 110 spiracles Oil tliese 



rolled tracheae ; e, envelope ; /pedi- ^^^ thoracic segments ill Lepi- 

 cel ; //•, trachea. (After CToniu.) " , '■ 



dopterous larvae). Cionin has 

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



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



