50 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 63 



ures irregularly distributed, as are the isolated slits. A few of Hicks' 

 vesicles exist on the mouth parts but none is found on the sternum 

 and abdomen, except those in the sting", which might be compared 

 in position to the lyriform organs on the spinnerets of spiders. 

 Since spiders have no wings, possibly all the slits on the mouth parts, 

 sternum, pedicle, and the ones on the abdomen exclusive of those on 

 the spinnerets, replace all the pores that exist on the wings of insects. 



A great difference in the number of groups and isolated slits was 

 found in the different species. The spiders that hunt for their food 

 and use no webs in capturing their prey, without exception have the 

 most slits, while those that live in caves and catch their food entirely 

 by means of webs have the least number. The common cobweb 

 spider ( Thcridium tepidariorum) catches its prey wholly by webs ; 

 it does not live in caves and may be considered as intermediate be- 

 tween hunting spiders with highly developed lyriform organs and 

 cave spiders with degenerated lyriform organs. By counting all 

 the slits on the surface of this cobweb spider, we find that an 

 average spider possesses 1,770 slits, whereas considering an average 

 worker bee, we have already seen that it possesses 2,270 pores. As 

 stated by the other observers, lyriform organs have now been found 

 in 7 of the 9 orders belonging to the Arachnida. 



A lyriform organ is composed usually of several single slits which 

 lie side by side and more or less parallel with each other. This 

 group of slits is generally surrounded by a border, produced by a 

 difference in pigmentation, which gives the lyre shape to the organ. 

 Inside the border the pigmentation is usually much lighter than out- 

 side ; hence a group appears as a light spot, while the superficial 

 appearance of a slit reminds one of a long, slightly bent spindle that 

 has an aperture either at the center or nearer one end than the other. 

 A cross section of a slit shows that the aperture passes entirely 

 through the cuticula and unites with the sense fiber of a large spin- 

 dlelike sense cell lying at the base of the thick hypodermis. Thus 

 a cross section of a slit with its sense fiber may be likened to a greatly 

 flattened funnel. The innervation of a lyriform organ is identical 

 with that of a group of olfactory pores, except that in the former 

 the sense fibers unite with the base of the apertures, whereas in the 

 latter the sense fibers connect with the top of the apertures. 



So far as the waiter knows, structures similar to lyriform organs 

 and Hicks' pores have never been looked for in crustaceans. It is 

 very probable, however, that this class of arthropods possesses some 

 kind of organs that take the place of lyriform organs and Hicks' 

 pores. 



