Sensor ji Hairs 37 



position' which the lateral eyes occupy in Pedipalpi. According to Michael a pair of remark- 

 able haii-s ai-e found in Oril)atida:>, to which he gives the name of " pseudo-stigmatic organs." 

 Michael gives (a, pp. 186 — 190) a careful general description of these hairs, which are very 

 different in different forms, and in some cases i-emarkably built, in addition to which he men- 

 tions and figures them in treating of the different species. Michael considers them to be 

 probably organs of sense, and we are of opinion that they may naturally be compared to those 

 hairs serving purposes of sensation, which occur in Koeneiiia and in Sironini : and they occupy 

 a somewhat similar, though more dorsal, position on cephalothorax. In the other two sub- 

 orders of Opiliones nearly all the species possess well developed eyes, nor have we found any 

 such hairs as those we have described in any of the species which we have examined. In 

 each of the two sub-orders a few blind species are known, but we are not acquainted with 

 them. 



In all the Cyphophthalmi which we have dissected, Stylocellus, Parcellia, Siro, and Para- 

 siro, we have found a pair of frontal bristles destined for sensation, and as we have been able 

 to ascertain their presence in Pettalws hrevicauda, without dissection, we believe that they are 

 found throughout that sub-order. The most characteristic form of the.se sense hairs we found 

 in Purcellia (PL IV., fig. 1 a, s), where they are placed a little behind the anterior margin of 

 cephalothorax, near the posterior extremity of the median excavation, at a small distance from 

 each other : they are shorter but conspicuously thicker than the small bristles near them, 

 from which they may be distinguished also by their shape, as they are almost cylindrical, 

 abruptly pointed at the apex. In a specimen not fully grown we found them well developed, 

 only more gradually jwinted. In Stylocellus Beccarii (PI. I., fig. 1 c, s) these sense hairs stand 

 somewhat farther from the anterior edge of cephalothorax ; they are shorter, proportionately 

 thicker, and fairly evenly conical. In Siro duricorius these hairs are placed close together, 

 at the anterior edge itself, and as they taper more gradually towards the apex, they are 

 more like ordinary bristles, but are nevertheless easily distinguished from them. Also with 

 regard to this pair of sense hairs, we may recall that Grassi and we ourselves have 

 examined a hair of that kind in the blind Koenenia mirabilis, which is of very peculiar 

 shape, as it were bifurcate, and placed on the front in the middle line above the bases of 

 antennse. We have searched for a similar pair of hairs developed for sensation in a few 

 representatives of the two other sub-orders of Opiliones, but in vain ; and although it would 

 not in itself be unreasonable to expect their presence, we believe that we may with tolerable 

 certainty affirm that no such hairs are found in other Opiliones. 



Finally, we found sensory hairs on the donsal .side of tarsus of the two anterior pairs 

 of legs, but only on these pairs. The hairs are met with in all species similarly built in 

 both sexes, and also in young specimens of Purcellia. Generally about half a score or a 

 few more of them are found, scattered near the middle line on the distal half of each 

 tarsus, in some cases on a considerably larger portion ; but in the remaining shorter or 

 longer portion of tarsus, near its proximal extremity, they are never found. In Ogovia and 

 Pettalus their number is reduced to from four to seven on each tarsus. These hairs are always 

 easily recognized amongst the ordinary hairs or bristles, being light of colour, short or of 

 medium length, rather stout and of a peculiar shape. They are always more or less curved 

 and with the end obtuse, whilst the surrounding hairs or bristles terminate in a long and 



' In a subsequent paper one of us (H. J. Hansen, c, of two, three or four such hairs is found where the single 

 p. 20-3) has shown that in other species of Koenenia a bundle hair mentioned is placed in K. mirabilis. 



