vii] PUPAE AND THEIR MODIFICATIONS 83 



(Abraxas grossulanata) and the pupae of various 

 leaf-beetles. Others again spin together the edges 

 of leaves with connecting silken threads. The grubs 

 of bees and wasps which are reared in the comb- 

 chambers of their nests seal up the opening of the 

 chamber with a lid, partly silk (fig. 18 GO) and partly 

 excretion, when ready to pass into the pupal state 

 An additional external 'capping' may be also sup- 

 plied by the workers. 



The pupae of butterflies are especially interesting, 

 as illustrating the extreme reduction of the silken 

 cocoon. The pupa of a ' swallowtail ' (Papilionid) or 

 a 'white' (Pierid) butterfly (fig. 23) may be found 

 attached to a twig of its food-plant or to a wall, in 

 an upright position, its tail fastened to a pad of silk 

 and a slender silken girdle encircling its thorax. The 

 pupa of a ' Tortoiseshell ' or 'Admiral' (Xymphalid) 

 butterfly hangs head downwards from a twig, sup- 

 ported only by the tail-pad of silk, which, useless as 

 a shelter, serves only for attachment. The pupa is 

 fastened to this pad by a spiny hook or process, the 

 cremastcr (fig. 23 cr\ on the last abdominal segment. 

 The cremaster is a characteristic structure in the 

 pupa of a moth or butterfly. C. Y. Riley (1880) and 

 W. Hatchett- Jackson (1890) have shown that it cor- 

 responds with a spiny area, the suranal plate, which 

 lies above the opening of the caterpillar's intestine. 

 The means by which the suspended pupa of a 



6-2 



