THE EXTEkXAL STRUCTURE OF ANTS. 



27 



turned slightly downward or inward so that it may scrape back and 

 forth over the file (sir) when the two segments are moved on 

 each other and thereby produce a sound of very high pitch. The 

 file is, in all probability, merely a local specialization of the fine, 

 polygonal elevations or asperities which cover the adjacent portions 

 of the segment and are so characteristic of the chitinous invest- 

 ment of many parts of the body. Each of these minute elevations is 

 evidently secreted by one of the hypodermal chitinogenous cells. 

 Sharp found great diversity in the structure of the stridulatory organ 

 both among the different species and in the castes of the same species. 



wv 



FIG. 12. Stridulatory organ of Myrmica levinodis. (Janet.) A. Surface view of 

 right half of the organ ; sir, stridulatory surface : /. lateral, reticulate surface ; so, 

 sense-organs; in. tendon of muscle; ap, lateral apophysis ; r, radiating rugae at base 

 lit' first gastric segment. B, Median sagittal section of organ; str, stridulatory surface- 

 at extreme anterior border of first gastric segment ; p, edge of postpetiole which 

 scratches the stridulatory file str. 



An interesting modification was found in an Australian Myrmicine ant 

 of the genus Siina, which has the file divided into two parts, one con- 

 sisting of coarse, the other of fine, ridges, and Sharp remarks that " a 

 stridulatory performance by this insect might produce very extraor- 

 dinary effects." Janet, in his studies of Myrmica rubra, calls attention 

 to the fact that there are accumulations of chitinous asperities at various 

 widely separated regions of the ant's body, especially on articulations 

 which might, by their movements, produce sounds. I'ut the true 

 stridulatory organs he finds to be situated where they were seen by 



