GLANDULAR HAIRS AND SPINES 



191 



the larvae of Pterophoridae. They are either club-shaped, or vari- 

 ously forked at the end (Fig. 214, B, a). They are usually replaced 

 after the first larval moult by ordinary, simple, solid, pointed setae, 

 and their use in caterpillars is as yet unknown. Whether these 

 hairs, as seems most probable, arise from a specialized glandular 

 hypodermal cell, or not, has not yet been discovered. 



These temporary fine glandular hairs are probably the homologues 

 of the larger true glandular bristles and spines of the later stages of 

 certain lepidopterous larvae, which are brightly colored and lead an 

 exposed life, living through a large part of the summer. In these 

 structures the bristles or spines are hollow, filled with a poisonous 

 secretion formed in a single large, or several smaller specialized 



C. 



FIG. 215. A, group of set arising from a subdorsal tubercle: cut, the cuticle; hy, the hypo- 

 dermis; c, the enlarg-ed and specialized cells of the hypoderrais which secrete the spines them- 

 selves ; pglc, the nuclei which secrete the venomous fluid which fills the cavity of the seta (*), seen 

 at p in a broken spine. B, a short entire, and a long broken seta (*-/>); pglc, four poison cells ; 

 p, the poison in the hollow of the spine. 



hypodermal cells situated under the base of the spine. In the 

 venomous spines of Lagoa crispata the poisonous fluid in the larger 

 spines (Figs. 215, C, 216, b) is secreted in several large cells situated 

 at the base of the spine, and this is the usual form. In the finer 

 spines of a large tubercle (Figs. 215, A, 216) there appears to be a 

 differentiation of the hypodermal cells into two kinds, the large, 

 basal deep-seated, setigenous cells (216, sc) and the poison-secreting 

 nuclei (216, pylc) situated nearer the base of the setae. The spines 

 being filled with poison and breaking into bits in the skin of the 

 hands or neck, caxise great irritation and smarting. These nettling 

 or poisonous hairs or spines are especially venomous in the larva of 



