630 TEXT-BOOK OF ENTOMOLOGY 



uniting the fibres of the cocoon. " This liquid is composed in great part of 

 bombycic acid." (Amer. Naturalist, i, p. 33.) 



The pupa of the dipterous genus Sciara (<S r . ocellaris 0. S.) resembles a tineid 

 pupa, and before transform ing emerges for about two-thirds of its length from 

 the cocoon ; the pupa-skin remaining firmly attached in this position. 1 



Certain hymenopterous pupse are provided with temporary deciduous conical 

 processes. Thus we have observed in the pupa of Ehopalum pedicellatum two 

 very prominent acute tubercles between the eyes (h, Fig. 592). As the cocoon 

 is very slight, these may be of use either in extracting itself from the silken 

 threads or in pushing its way along before emerging from the tunnel in the stem 

 of plants. (See also p. 611.) 



c. The cremaster 



Although this structure is in general confined to lepidopterous 

 pupae, and is not always present even in them, since it is purely 

 adaptive in its nature, yet on account of its singular mode of devel- 

 opment from the larval organs, and the accompanying changes in the 

 pupal abdomen, it should be mentioned in this connection. The 

 cremaster is the stout, triangular, flattened, terminal spine of _the 

 abdomen, which aids the pupa in working its way out of the earth 

 when the pupa is subterranean, or in the pupa of silk-spinning cater- 

 pillars its armature of secondary hooks and curved setae enables it 

 to retain its hold on the threads of the interior of its cocoon after 

 the pupa has partially emerged from the cocoon, restraining it, as 

 Chapman well says, "at precisely that degree of emergence from 

 the cocoon that is most desirable." He also informs us that while 

 in the "pupce incompletce the cremaster is attached to an extensible 

 cable, which always allows some emergence of the pupa, in the 

 pupae obtectae there is no doubt but that in such cases as the Ich- 

 thyurae, Acronyctae, and many others, it retains the pupal case in 

 the same position within the cocoon that the living pupa occupied; 

 this is also very usually the case in the Geometrae and in the higher 

 tineids (my pyraloids)." 



In many of the more general! z?d moths there is no cremaster (Micropteryx, 

 Gracilaria, Prodoxus, Tantura, Talfeporia, Psychidre, Ilepialidte, Zeuzera, Nola, 

 Harrisina), though in Tischcria and Talieporia (Fig. 590, but not in Solenobia) 

 and Psychidre, two stout terminal spines perform the office of a cremaster, or 

 there are simply curved setre on the rounded, unarmed end of the abdomen, as 

 in Solenobia. 



In the obtected Lepidoptera, for example in such a group as the Notodontidfe, 

 where the cremaster is present, though variable in shape, it may from disuse, 

 owing to the dense cocoon, be without the spines and hooks in Cerura, or 

 the cremaster itself is entirely wanting in Gluphisia, and only partially devel- 



i Riley's Report for 1892, p. 203. 



