396 PROCEEDINGS OF THE ACADEMY OF [May, 



only six in the males on the right side: on the left side ten times in 

 the females to nine times in the males. ( )rgan No. 3 of the females 

 on both sides is much oftener diffused than is that of the males. The 

 only other striking difference is the greater number of isolated slits 

 on both legs of the females. In two cases in the males a simnle organ 

 takes the place of a compound one, and in the legs on either side in 

 both sexes an organ is occasionally absent. In all other cases in which 

 I have carefully examined more than one specimen of the same species, 

 I have not found any individual variations of more importance than 

 the above. Hence we see that the organs are pretty constant on both 

 sides of the body in both sexes, while the number of single slits varies 

 considerably both individually and sexually. 



By carefully comparing the males and females of the same species 

 we see that there are no variations except what can be considered as 

 Individual variations. The only difference worth mentioning is the 

 great number of single slits on the last joint of the palps in the 

 males (fig. 9), while none or only a few are found at the same place 

 in the females. By referring to the totals in the table one sees that 

 the males of Th. tepidariorum and Phidippus have one compound 

 ■organ less than the females ; the male of Pkolcus two less ; the male of 

 Troglohyphantes three less; an equal number in both sexes of Linyphia; 

 the male of Lgcosa lepida one more, and the male of Agalena three 

 more organs than the female. 



■(d) Conclusions. 



Now, to interpret the meaning of the totals in the table, it is evident 

 that relationships play no part at all, for there is a great range of 

 variation within a genus or family. Therefore these organs are not 

 useful for taxonomy. As already stated individual and sexual varia- 

 tions are very slight. Specific variations are also very slight as seen 

 in the two Lycosas, and in the three species of Theridium. Generic 

 differences are not very great when the various genera have a similar 

 habitat, as in Moggridgea, Hermacha, and Evagrus; a less variation 

 between Tetragnatha and Epiera, but the same number of organs in 

 Dysdera and Ariadna; however when the habitat is dark and damp 

 the number of compound organs is usually much less as shown in the 

 linyphiid cave forms and in a linyphiid littoral form, Grammonota. 

 The most important variation in the morphology of the lyriform organs 

 can certainly be correlated with the method of capturing food. In 

 the manner of securing food, spiders are divided into three classes as 

 follows: (1) The hunters are those which wander about in search of 



