November 17, 1893.] 



SCIENCE 



273 



THE SENSE-ORGANS ON THE LEGS OF OUR WHITE 

 ANTS, TERMES FLAVIPES, KOLL. 



BY DR. ALPBED C. STOKES, TRENTON, N. J. 



In an eyeless creature that habitually shuns some in- 

 fluence in the light, and lives in subterranean passages, 

 or in tunnels or dark fissures within decaying wood, we 

 should hope and rather expect, if we considered the mat- 

 ter solely from the human standpoint, to find either an 

 extra number of sense-organs or a supply of an unusual 

 variety, as a compensation for the absence of sight and 

 for the limitations of a restricted environment. Such 

 human expectations would be realized in the case of the 

 white ants, Terries flavipes, so common within the rotting 

 stumjjs and the fallen branches of our damp woods, for 

 these Platyptora possess what may be considered to be an 

 ample exchange for sight, for they hare on all of the six 

 legs a wonderful number and variety of sense-organs, 

 which should certainly meet the needs of «. peculiar life, 

 as they doubtless do. 



It is generally agreed among naturalists that certain 

 insects, perhaj)s the greater number, possess some 

 senses different from any owned by man and of which we 

 therefore can have no idea. Sir John Lubbock says, "It 

 is, I think, generally assumed, not only that the world 

 really exists as we see it, but that it appears to other an- 

 imals pretty much as it does to us. A little consideration, 

 however, is sufficient to show that this is very far from 

 being certain, or even probable." 



On each of the legs of Terme» flavipes there are seven 

 organs which are plainly sense-organs, with three forms 

 of appendages which may be sensory, but are probably 

 ornamental only. The blind, subterranean Termed, then, 

 with six legs and with seven sense-organs on each, 

 is right well j)i"epared for whatever may happen, 

 even for the forceps of the predatory micros- 

 copist. The forceps conquers in the end, but the 

 insects seem to feel its presence before it touches them, 

 retreating and sometimes backing away from it as from 

 some obnoxious object. Yet upon this ajsparent fact I 

 should put no great reliance, as the observation was made 

 with a single nest and late in the season, although the 

 lateness of the season would probably have no effect, ex- 

 cept to render impossible, as it did, a repetition of the 

 experiment. It may, therefore, have been an event 

 "viewed unequally." 



The appendages referred to as being doubtfully sensory 

 are mere elevations of the chitinous walls, ornamental in 

 their arrangement, minute in size, and if j)ossessiug any 

 special nervous connections, these have escajDed my notice. 

 The appendages, or ornaments, vary much in appearance 

 on the coxa, the trochanter and the tarsus, the femoral 

 and the tibial ones being similar to those on the coxa. On 

 the latter the elevations are simply aculeate, the aculei 

 being exceedingly minute; on the trochanter and on the 

 femur they take the form of minute prickles, which, at 

 first glance, appear to mark out the impressions of the 

 chitinogenous cells, as in Fig. 1, from the femur; on the 

 tibia the elevations become still more aculeate (Fig. 2); 

 they are more widely separated, and the delicately ele- 

 vated ridge which bears them gives the markings much 

 the aspect of irregular, thick-edged scales, esi^ecially at 

 the distal extremity, as in Fig. 3; on the tarsus the change 

 from^these clusters of aculei is abrupt, more or less semi- 

 circular scales, with thickened and elevated margins taking 

 their place, as in Fig. -4, the edges of these being some- 

 times minutely denticulate. Viallanes, sj)eaking of the 

 situation of the sensory hairs of insects in reference to the 

 chitinogenous cells, says that there are "two kinds of hairs, 

 distinguished by their size and structure. The smaller 

 spring from the boundary between contiguous polygonal 



areas, and have no sensory character. The larger ones 

 occupy unusually large areas, surmount chitinogenous 

 cells of corresponding size, and receive a special nervous 

 supply." It is more than probable, therefore, that these 

 minute appendages have in no filace a significance differ- 

 ent from that possessed by the minute elevations so com- 

 mon on the exo-skeleton of so many insects. But to notice 

 the different form and arrangement on the different por- 

 tions of the leg is at least interesting and suggestive. 



The chitinous bristles, or "hairs" (Fig. G), have here the 

 usual form, and the structure described by Viallanes, be- 

 ing slightly constricted at base and inserted in a hemi- 

 spherical dejjression as a socket-joint, and furnished with 

 a nerve-fibre, of which Viallanes saj s: "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 chitino- 

 genous cell, whose 23rotoplasm 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."* On the legs of Termes flavipes these 

 are, as elsewhere, sense-organs of great delicacy, with a 

 sense of touch probably as sensitive as that of man 

 himself. 



In the same list with these sensory hairs may be men- 

 tioned organs of a similar character and of apparently 

 great importance to the insect, which are found at the 

 distal extremity of each tibia, each leg of the second and 

 of the third pair bearing two, while those of the first jDair 

 have three. They are stout thorns, or spurs, projecting, 

 in the first or anterior pair, two from the lower lateral 

 margin of the tibia, with one from the upper lateral border, 

 as shown in Fig. 9, where the other sensory hairs have 

 been omitted. 



They are conical organs, measuring about 1-450 inch in 

 length, and are, during life, well supplied with nerve- 

 substance. But that which gives them their unique char- 

 acter is the presence of a more or less circular aperture 

 near the basal or tibial j)ortion of the thick wall, as shown 

 in Fig. 9, and more in detail by Fig. 15, each insect thus 

 possessing no less than fourteen of these peculiar perfora- 

 tions. The circular aperture is externally surrounded bv 

 a thick-walled, elevated, marginal ring, and across it, ap- 

 parently at the level of the general surface of the tibial 

 wall, extends a delicate membrane, suijplied with a rather 

 conspicuous, centrally disposed nerve-fibre, as shown in 

 Pig. 15, where a nerve is also delineated as passing from 

 the tissues within the hollow of the spur to the mass of 

 nerve-tissue which is here retracted from the walls, prob- 

 ably by the ijrocesses of preparation. "Within the mass 

 thus withdrawn ganglion-cells are plainly visible. 



What may be the function of these fourteen organs, 

 which are doubtless sense-organs of importance, must be 

 left to the reader to explain. I do not know that they 

 have been previously observed; yet it is more than pos- 

 sible that I may have overlooked some parts of the scat- 

 tered literature of the general subject. If any plausible 

 conjectures have been published in regard to the function 

 of these or of similar organs, I should be pleased to know 

 what they are, although all such statements must neces- 

 sarily be conjectural. It is easy to state that certain 

 depressions on the antenna of a bee are auditory or 

 olfactorj', but it is quite another matter to do more than 

 to make the assertion. When it comes to the making of 

 experiments to learn the actual function of these minute 

 structures, the obstacles met with are practically insur- 

 mountable. But if these tibial spurs of the white ants, 

 with their prominent basal apertures, have been previously 

 studied, and if any probable guessing has been done as to 



*Cf. "The Cockroach,"' by Miall and Denny, p. 30. 



