HANSEN: EXTKRNAL SENSORY ORGANS IN ARACHNIDA. 245 



ally with a number of extremely minute hairs. On the 

 places, where the lateral eyes should be looked for, one finds 

 either a single organ or a bundle of two to four such or- 

 gans; each is oblong lancet-shaped with somewhat scarce 

 and extremely short pubescense. These interesting organs, 

 which had been discovered in Koenenia mirabilis by Grassi, 

 was later found in several species, described and figured 

 (H. J. Hansen, b, p. 204 — 5). — The Palpigradi possess other 

 setœ which, in my opinion, probably have a sensory function. 

 One such seta is found on the upper side of the metatarsus 

 of the last pair of legs; another seta of different shape exists 

 on the outer side of third metatarsal joint of first pair of 

 legs; a more special description with figures of these setae is 

 found in my last-named paper (p. 206 — 7). 



Among the Araneœ I have specially examined Epeira 

 diademata Clerck without observing other sensory hairs than 

 the trichobothria. But the order is extremely large, compris- 

 ing many families partly rather different in various features. 

 And VV. Wagner (1888) has mentioned hairs which have a 

 nerve entering into their basal part and have a tactile func- 

 tion, but are not trichobothria, as their mode of insertion is 

 much more simple; he pronounced that such hairs exist in 

 all Araneae, but unfortunately did not say anything as to 

 their distribution on the animals. I am inclined to think that 

 a special investigation of types of all families may yield in- 

 teresting results, but for various reasons the examination will 

 be difficult and protracted. 



Of the sensory hairs or setae in the rich and varied or- 

 der Opiliones a somewhat detailed account has been given 

 by me in 1904 (Hansen & Sorensen b, p. 36 — 40). Here 

 a short abstract may be sufficient. 



The genera belonging to the suborder Cyphophthalmi 

 are blind excepting the genus Stylocelltis Westw., which has 

 a pair of sublateral eyes. Exactly on the spot where the 

 eye is placed in Stylocelhis, we find in Purcellia illnstrans 

 H. J. H. & W. S. a seta which is many times longer and 

 thicker than the very fine and short hairs scattered on 

 the upper side of the céphalothorax; besides, this seta is in- 

 serted on a small hollow knot. In Pettalus brevicaiida PoCK. 



