261] NOCTUID LARVAE— RIPLEY 19 



situated on the membranous end of the proximal segment. A terminal 

 seta is also borne by the distal segment. These two setae are apparently 

 of universal occurrence in caterpillars. 



SPINNERET 



The spinneret is located on the mesal portion of the membrane on the 

 caudal aspect between the palpigers. The cephalic and lateral portions of 

 its proximal end are surrounded by a semi-circular sclerite of varying width 

 and shape, resembhng the palpiger, although much smaller. A pair of 

 sensoria are borne on the caudal aspect of this structure usually at its 

 mesal ends. These sensoria are much smaller than those of the palpiger. 

 A fold of membrane often extends distad from this sclerite surrounding the 

 proximal end of the spinning organ, the tube through which the silk is 

 extruded. This fold is usually much wider on the cephalic aspect, where it 

 may assume the form of a long plate reaching nearly to the end of the 

 spinning organ. Occasionally it is entirely chitinized, when it is indis- 

 tinguishable from the proximal sclerite. The spinning organ varies exten- 

 sively, presenting a great diversity of size, form, and modification. It 

 ranges from entirely membranous to largely chitinized, from very long and 

 tubular to short and flat. The silk-duct opens at its distal extremity. 



Wide differences of opinion have been expressed as to the homology of 

 this peculiar organ. A number of workers, represented by Packard, regard 

 it as a modified h\-popharynx, whereas Berlese and Dampf believe it to be 

 formed of the fused glossae and paraglossae, the latter investigator even 

 venturing to homologize the proximal sclerite and fold with the paraglossa 

 and the spinning organ with the fused glossae. It seems very probable to 

 the author, on the other hand, that this structure has developed secon- 

 darily. Those who regard it as hj^opharynx appear to be misled by insuf- 

 ficient data. The silk-glands of lepidopterous larvae have reasonably been 

 supposed to be the homologues of the salivary glands of the adults. Lucas 

 subscribes to the same homology in the Trichoptera. The salivary glands 

 of adult insects, so far as known to these investigators, opened at the base 

 of the hypopharynx. Therefore, they reasoned, the silk-glands of cater- 

 pillars, which they regarded as the homologues of salivary glands generally, 

 would presumably open on the hypopharynx, giving rise to the belief that 

 this structure had been modified into a spinneret. MacGillivray has shown, 

 however, that the salivary ducts of the Entopteraria open on the glossae of 

 the labium, wherever these structures can be identified, and not at the 

 base of the hypopharynx as in the Exopteraria, which was evidently the 

 only condition known to these earlier workers. It seems questionable, 

 therefore, whether these glands are homologous in the two superorders. 

 However this may be, no evidence remains in support of the old view that 



