THE EXTERNAL MORPHOLOGY OP THE LEPIDOPTEROUS PUPA. 51 



cremaster, such as the terminal row of spines in Tinea, the two stout 

 spines in Tisclieria, 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 iEgerians. These various pro- 

 jections and spines, besides acting as anchors and grappling hooks, in 

 some cases serve to resist strains and blows, and have, undoubtedly, 

 like the armature in the larvae and imagines of other insects, arisen in 

 response to intermittent or occasional pressure, stress, or impact." 



With regard to the various structures observed in the butterfly 

 cremaster (e.g., as exhibited in Nymphalids), and that take part in the 

 suspension of these pupae, the following may be mentioned : (1) The 

 dorsal ridge. (2) The ventral ridge. (3) The cremastral hook-pad. 

 (4) The sustainers (sustentores). (5) The sustentor ridges. (6) The anal 

 prominences. The " cremastral hook-pad," Eiley says, is "thickly 

 studded with minute but stout hooks, which are sometimes compound 

 or furnished with barbs, very much as are some of our fishing-hooks, 

 and which are most admirably adapted for the purpose for which they 

 are intended." The " sustainers " or " sustentors " are homologised 

 by Riley with the soles or plantae of the anal prolegs, and the " sus- 

 tentor ridges " with the limbs, but Jackson disagrees with this, believ- 

 ing that the "sustentor ridges" and "sustentors" are probably 

 peculiar developments of the body of the 10th somite, found only in 

 some Lepidoptera. He further states that the eminences (or "rectal 

 prominences," as they are called by Eiley) on either side of the anal 

 furrow represent the prolegs. Packard agrees with Jackson, and states 

 that the " sustentors " and their ridges are not to be found in the pupae 

 of the more generalised moths, whilst the vestiges of the anal legs are 

 almost invariably present, their absence in the pupae of Nola and 

 Harrisina being noteworthy. The "sustentors" assume various 

 forms, but are always directed forwards so as easily to catch hold of 

 the retaining membrane. The " sustentor ridges " form quite a deep 

 notch which doubtless assists in catching hold of the larval skin in 

 the efforts to attach the cremaster. Riley states that it is principally 

 by the leverage obtained by the hooking of the sustainers in the 

 retaining membrane, which acts as a swimming fulcrum, that the 

 chrysalis is prevented from falling, after the cremaster is withdrawn 

 from the larval skin. It is also " principally by this same means that 

 it is enabled to reach the silk with the cremastral hook-pads." Packard 

 goes so far as to give the cremaster systematic or classifactory value. 

 He says that "the cremaster affords excellent generic and specific 

 characters. It is present in the subterranean pupa of Datana, and is 

 of use in aiding the pupa to reach the surface of the ground. It is 

 very large and acute in the subterranean pupae of Ceratocampidae and 

 Sphingids. It is evident that, in the presence or absence of the 

 cremaster, and in its shape, and in the number of hooks and their 

 shape, we have a set of very plastic characters (though excellent for 

 distinguishing genera and species) whose variability and plasticity is 

 due to the varying habits of the pupa, whether living above or under 

 ground, whether protected by a very thin, loose, net-like cocoon, or by 

 a solid double one like that of Centra or of the silkworms." The 

 cremaster of the Pterophorid pupa is peculiar in that it consists of an 

 anal and a forward portion, but is paralleled by those of the Elachistids, 



