380 PROCEEDINGS OF THE ACADEMY OF [May, 



ventral and the other on the dorsal side. In fact each one seems to lie 

 directly beneath a lyriform organ. The blood plasm (b. p.) and blood 

 corpuscles (b. c.) can readily be distinguished in both the artery 

 and sinuses. 



The connective tissue (con. t.) which stains very faintly occupies 

 all the remaining space in the leg. Its nuclei (con. t. n.) which are 

 very conspicuous are about one-half as large as those of the hypo- 

 derm is. 



Fig. 2 is a longitudinal-transverse diagram of the distal end of a 

 femur showing the anatomy of the leg with the innervation of the 

 lyriform organs, the fixed tactile hairs (t. h.) and the muscles which 

 control the movable tactile hairs (mov. h.). 



2. Disposition. 

 (a) Theridium tepidariorum Koch. 



In making a comparative study of the lyriform organs of Araneads, 

 I have used thirty-nine different species representing twenty-seven 

 of the thirty-eight families recognized by Simon (1892). Since 

 Th. tepidariorum is most conveniently studied, I shall describe its 

 lyriform organs in detail and then state the variations found in the 

 •other species after the explanation of the table on page 394. See 

 figs. 13 and 14. 



The legs and palps may be divided for description into four surfaces. 

 The organs, to begin with the one on the coxa of each leg and palp, 

 may be numbered from 1 to 13 with No. 13 on the metatarsus of each 

 leg. In Th. tepidariorum there is a constant number of thirteen 

 organs on each leg; four of this thirteen are on the dorsal, three on 

 the posterior, two on the anterior, and four on the ventral surface. 

 Each palp has only seven organs, three of which are on the dorsal and 

 the other four are on the ventral surface. Each cheliceion has a 

 constant number of four organs, No. 14 and 15 of which lie on the 

 ventral and No. 16 and 17 on the dorsal surface. There is always a 

 constant number of two organs located on the dorsal side of the pedicle, 

 one of these may be called No. 18. The single isolated slits are found 

 more or less regularly distributed on all the appendages, sternum, 

 cephalothoracic shield and on the ventral side of the abdomen (figs. 

 13, 14). 



Every organ has a constant position except the three on the tro- 

 chanter and the one on the coxa. The latter organ occurs either on 

 the ventral or posterior side of the joint. The organs on the tro- 

 chanter rotate around the segment and sometimes the same organ 



