SENSORY SETJE OF TARANTULA AND SOME OF 

 ITS RELATIVES 



WILLIAM A. HILTON 



The general sensory terminations of insects are found in hairs. These 

 setiK are of about the same type throughout the group and consist of hollow 

 extensions of chitin which may be microscopic or much larger. The base of 

 the hair is usually movably, articulated in a chitinous ring. Below the cuticle 

 and level with the liypodermal cells, there is at the base of each hair a larger 

 "trichogen" or hair-producing cell. Sensory structures similar to sette in 

 insects have been described and figured in the Crustacea and some of these 

 have been found with the bases of the hairs solid so that nerve fibres cannot 

 penetrate very far into the hairs. Judging from methylene blue preparations 



Figure 254 



Sketch of a section throuKli a body scum- iiair of an insect, showing the penetration 

 of a nerve liljre into the l)ase of the hair. 



studied in section (Hilton '02), the nerve fibres of insects go only to the 

 basal portions of the hairs and there terminate on one side (Figure 254). 



In a study of the hairs of insects, spiders and other arthropods, it becomes 

 necessary to distinguish l)et\veen the hollow sensory setie and tlie solid eleva- 

 tions of the cuticle which are either very uuicli smaller or very much larger 

 and heavier. These minute hair-like elevations and the larger spines or 

 projections seem to he hirgcly for protection. 'I'liey are undoubtedly also for 



