THE INTERNAL STRUCTURE OF ANTS. 



61 



object the tactile impulse is evidently transmitted to the nerve through 

 the movement of the bulbous base in its cup-shaped socket. There is, 

 therefore, no essential difference between the tactile function of the 

 hairs of ants and the analogous structure in mammals. 



Olfactory and Gustatory Sensillae. It seems to be impossible to 

 distinguish between these organs in insects, although it may be asserted 

 that the organs of smell are situated mainly or exclusively on the 

 antennae, whereas, those of taste are found on the mouth-parts, espe- 

 cially on the maxilla? and labium and their palpi. The antennary 

 sensillae of ants have been studied by Hicks (1859), Leydig (1860)., 

 Forel (1874, 1884), Lubbock '(1877), Kraepelin (1883), and more 

 recently by Krause (1907). From the researches of these authors it 

 appears that in addition to numerous tactile hairs like those described 

 above, there are four more modified types of sensillae which have been 

 more or less definitely connected with an olfactory function. These do 



FIG. 32. Subdiagrammatic section of the antennal sense-organs of an ant. 

 (Kraepelin.) a, Basiconic sensilla ; b, trichodeal sensilla, or tactile hair; c, coeloconic 

 sensilla ; d, ampullaceous sensilla; /, flask-shaped sensilla; g and h, openings of same 

 on surface of antenna ; i, gland cells ; k, chitinous integument. 



not occur on the scape and first funicular joint of the antennae, but 

 only on the remaining joints and especially on the enlarged terminal 

 joint, which possesses by far the greatest number of all the various 

 s.ensillae. The following is a very brief description of these extra- 

 ordinary structures : 



(a) Clubs of Ford (now called basiconic sensillae by Berlese). 

 These resemble the tactile hairs, but are conical and immovable at the 

 base and their chitinous investment is exceedingly thin (Fig. 32, a}. 

 What corresponds to the cavity of the hair contains a dense bundle of 

 delicate protoplasmic threads, which are prolongations from as many 



