THE CRE MASTER 637 



oped in Notodonta. In the butterflies whose pupse are suspended (Suspensi), 

 the cremaster is especially well developed. Reference might here be made to 

 the temporary pupal structures in certain generalized moths, which take the 

 place of a cremaster, such as the transverse terminal row of spines in Tinea, 

 the two stout spines in Tischeria, and the dense rough integument and thickened 

 callosities of the pupal head and end of abdomen of Phassus, which bores in 

 trees with very hard wood ; also the numerous stout spines at the end and 

 sides of the abdomen in ^Egerians. These various projections and spines, be- 

 sides acting as anchors and grappling hooks, in some cases serve to resist strains 

 and blows, and have undoubtedly, like the armature in the larvse and imagines 

 of other insects, arisen in response to intermittent or occasional pressure, 

 stresses, and impacts. 



Mode of formation of the cremaster and suspension of the chrysalis in 

 butterflies. - - We are indebted to Riley l for an explanation of the 

 way the cremaster has originated, his observations having been 

 made on species of over a dozen genera of butterflies (Suspensi). 



He shows that the cremaster is the homologue of the suranal 

 plate of the larva. 2 The preliminary acts of the larva have been 

 observed by various authors since the days of Vallisneri, i.e. the 

 larva hanging by the end of the abdomen, turning up the anterior 

 part of the body in a more or less complete curve, and the skin 

 finally splitting from the head to the front edge of the metathoracic 

 segment, and being worked back in a shrivelled mass toward the 

 point of attachment. The critical feat, adds Riley, which has most 

 puzzled naturalists, is the independent attachment of the chrysalis 

 and the withdrawal from and riddance of the larval skin which such 

 attachment implies. Reaumur explained this in 1734 by the clutch- 

 ing of the larval skin between sutures of the terminal segments of 

 the chrysalis, and this is the case, though the sutures act in a some- 

 what different way. 



Before pupation the larva spins a mass or heap of silk, the shape of which is 

 like an inverted settee or a ship's knee, and "one of the most interesting acts of 

 the larva, preliminary to suspension, is the bending and working of the anal 

 parts in order to fasten the back of the (suranal) plate to the inside of the back 

 of the settee, while the crotchets of the legs are entangled in the more flattened 

 position or seat." 



In shedding the larval skin, the following parts are also shed, and have some 

 part to play in the act of suspension: i.e. 1st, the tracheal ligaments (Fig. 593, 

 ?), or the shed tracheae from the last or 9th pair of spiracles; 2d, the rectal 

 ligament (Fig. 593, rZ), or shed intestinal canal; 3d, the Osborne or retaining 



1 Philosophy of the pupation of butterflies, and particularly of Nymphalidse, by 

 Charles V. Riley. (PYoo. Amer. Assoc. Adv. Science, xxviii, Saratoga Meeting, 

 August, 1SSO, pp. 4.->5-4(S3.) 



2 The homology of the suranal plate of the larva with the cremaster of the pupa, 

 estahlishcil by Riley in 18SO, is also affirmed by Jackson (1888) and by Poulton, and 

 for some years we have been satisfied that this is the correct view; Professor 

 Hatchett-Jackson discovered it, he states, in 1876. 



