38 Sensory Hairs 



extremely fine point. The insertion of these sensory hairs is also rather different from tha 

 of the surrounding bristles. Round their point of insertion the skin is thinner, so that 

 this point is in a lower level, but they cannot well be described as inserted in the bottom of 

 small calicles, as is the case with another kind of hairs developed for sensation, which 

 are found in several other orders of Arachnida. In Pettalus, Purcellia, Sii'o and Pca-asiro 

 the}' (PI. v., fig. 2 /(, s) protrude considei'ably, and as they are at the same time of medium 

 length in the species of these genera, except in Pettalus brevicauda, they are very conspicuous, 

 when tarsus is viewed from the side. In Ogovia and Stylocellus (various figures on PI. I., 

 II., III.) they are comparatively short and at the same time more closely pressed against the 

 surface or more curved, so that they are very often not easily seen ; even a slight turning of 

 tarsus .suffices to hide them entirely. We are of opinion that these hairs must be organs of 

 feeling of some description. 



In (the male) Acantholophus ephippiatus C. L. Koch, which belongs to Phalangioidse, one or 

 two hairs developed for sensation are found on each of the last eight tarsal joints of the first 

 pair of legs, and of the last eleven tarsal joints of the second pair of legs, corresponding in 

 shape, colour, and mode of insertion to those which occur in Purcellia and others. On the 

 upper surface of the distal half of the last tarsal joint of the same two pairs of legs, as well 

 as on the upper portion of the terminal surface of this joint, several short, conical, near the 

 base thick, slightly curved or almost straight sensitive hairs occur, and on one or two of the 

 penultimate tarsal joints there is a similar hair. The last two pairs of legs are equipped 

 with both kinds of sensitive hair; we have not found any of the longer kind on the last 

 joint, but on each of the preceding three joints we have found one ; the number of the short 

 conical hairs is less than on the first two pairs of legs. As regards the last-named kind of 

 sensory hairs we refer, for the rest, to the description given below of those in Assamia 

 Sorensenii. — In Nemastoma luguhre O. Fr. Miiller the first pair of legs carry on the upper 

 surface of the last tarsal joint several sensory hairs, which are quite like those in Purcellia ; 

 some ai-e found on the first tarsal joint, and one solitary similar one on nearly all the other 

 joints. Tarsus of the second pair of legs is similarly equipped, but on several of the joints 

 the number of these hairs is somewhat larger. On the last tarsal joint of the last two pairs 

 of legs there are one or two sensorj' hairs, whilst a solitary one is found on one or two of the 

 more distal joints. Besides these, at least one of the short thick conical sensory hairs, which 

 here are almost abruptly bent in the middle, occurs on the distal portion of the terminal tarsal 

 joint of all the legs. Finally, a large number of somewhat different hairs are noticeable on 

 the proximal part of metatarsus of all the legs, whilst a minor number of the same occur on 

 the distal portion of the second metatarsus. These hairs are rather light in colour, much 

 curved and protruding ; they are at the same time finer than the tarsal sensory hairs, particularly 

 in their distal portion. In general appearance the.se hairs are to some extent intermediate 

 between the tarsal sensory hairs and ordinary hairs ; we do not venture to decide whether 

 they serve purposes of sensation, but it is not improbable. We have furthermore satisfied our- 

 selves of the presence of both kinds of sensory hairs on tarsi of the second and fourth pairs 

 of legs in a species of Dicranolasma belonging to Troguloidae ; but we have been obliged to 

 forego a systematic search for them, because we have not had an opportunity of dissecting a 

 specimen, which would be necessary on account of the sliortness of the first and third pairs of 

 legs. However, we have been able to point out the jiresence of such hairs in representatives 

 of three out of the four families comprised in the sub-order Palpatores, and, what is particularly 

 important, the two species, which we have been able to examine carefully, are good rejjresen- 



