ITS OUTER SKELETON. 



31 



The nerve* expands at the base of the hair into a spindle- 

 shaped, nucleated mass (bipolar ganglion-cell), from which issues 

 a filament which traverses the axis of the hair, piercing the 

 chitinogenous cell, whose protoplasm surrounds it with a sheath 

 which is continued to the tip of the hair. Such sensory hairs 

 are abundant in parts which are endowed with special sensibility. 



Fig. 9. Nerve -ending in skin of Stratiomys larva, h, hairs; b, their chitinous 

 base; c, nucleus of generating cell; y, ganglion cell, x 250. Copied 

 from Viallanes. 



Fig. 10. Diagram of sensory hair of Insect. Cc, chitinous cuticle ; h, hair ; c, its 

 generating cell ; g, ganglion cell ; bm, basement-membrane. 



The chitinous cuticle is often folded in so as to form a deep 

 pit, which, looked at from the inside of the body, resembles a 

 lever, or a hook. Such inward-directed processes serve chiefly 

 for the attachment of muscles, and are termed apodemes (apode- 

 matci). A simple example is afforded by the two glove-tips 

 which lie in the middle line of the under-surface of the thorax 

 (p. 58, and fig. 27). In other cases the pit is closed from the 



* Previously observed by Leydig in Corethra. 



