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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 77 



Sensory hairs mith suhhypodermal sense cells. — A good de- 

 scription of the structure of a setal sense organ innervated through 

 a suhhypodermal sense cell may be found in the recent paper by 

 Schneider (1923) on the sense organs of the cabbage worm {Picris 

 brassicce). The body of the caterpillar, according to Schneider, is 

 covered by small tuberculate hairs, all of which have sense cell con- 

 nections. Beneath the hair is a large trichogenous cell (fig. 11, 

 HrCl), with a large bent nucleus in its base, and having its distal 

 end prolonged into the hollow of the seta (Hr). Attached distally 

 to the hair membrane (HrMb) is a membrane cell (MbCl) which 

 surrounds the neck of the hair cell, and is continued to the basement 



BM 



Fig. II. — Example of the innervation of a larval tactile hair through 

 a subhypodermal sense cell. (Section of a body hair of a cabbage 

 worm, diagrammatic from Schneider, 1923.) 



membrane at one side of the hair cell. Several other hypodermal cells 

 (b), belonging to the walls of the tubercle, surround the trichogene 

 and the membrane cell. Since the hairs are renewed with each molt, 

 and are increased in size, the trichogenous cells vary in size and con- 

 tents according to the period in each instar, becoming large and full 

 before the molt, and shrinking following the molt. New hairs, also, 

 are added with each renewal of the cuticula. 



A bipolar sense cell (SCI) lies beneath the hypodermis in the im- 

 mediate neighborhood of each seta, and sends a long, slender distal 

 process (d) through the basement membrane (BM), along the side 

 of the trichogenous cell, toward the base of the hair. Presumably, 

 the process ends on the base of the hair, but Schneider says that 

 he failed to find its exact termination, though it never penetrates 



