HANSEN: EXTERNAL SENSORY ORGANS IN ARACHNIDA. 253 



Thysanura entotropha shall be interpreted as auditory organs, 

 there is scarcely any reason for not interpreting those on 

 the cerci of the Lepismatidae in the same way. As to more 

 special information on the occurrence of the trichobothria on 

 the appendages mentioned in various forms the reader is 

 referred to SlLVESTRl's above named paper and to some 

 other papers published from 1904 to 191 2 by the same 

 author. 



Outside the Thysanura trichobothria have not, as far 

 as I know, been discovered in any other order of Insects. 

 But many years ago, while arranging the collection of Forfi- 

 culidœ in the Copenhagen Museum, I found sensory hairs 

 rather similar to trichobothria on the forceps of a single 

 fine form, ChelisocJies superbus DOHKN. On the outer third 

 of the upper side near the base of each ramus of the for- 

 ceps is seen about six somewhat deep but only moderately 

 well limited impressions, and from the middle of each im- 

 pression projects an extremely fine, moderately long hair. 

 That we here have a kind of trichobothria with the calicle 

 only moderately developed is, in my opinion, quite certain. 

 — I was unable to find trichobothria on any other species 

 of Forficulidae in the Copenhagen Museum, but our collection 

 of this group is somewhat imperfect, and it is probable that 

 trichobothria can be found in some other tropical forms. — 

 In the Blattidge and Mantid?e I have examined the cerci 

 in vain. 



V. The trichobothria, their function, and 

 systematic value. 



In 1883 F. Dahl a, p. 267—270 discovered the tricho- 

 bothria on the legs and palps ofAraneje, and added that he 

 had also found them on the two joints of the large chelae in 

 Scorpions and Chelonethi. He did not name them tricho- 

 bothria but »Hörhaare», and two years after he (^) published 

 further observations on the occurrence of these auditory 

 hairs in families and genera of Aranese, with some new figures 

 of their structure. In order to prove that the hairs have 



