186 TARSAL-COMB IN SPIDERS. 



and the somewhat shaky character furnished by the small size and 

 weakness of the jaws, provides a quite natural character for distin- 

 guishing the above-named genera (with the exception of Ero 

 and Tkeridiosma, which are placed by M. Simon in other sections), 

 from all others, of the family Therldidce. We are not aware that 

 this character has been recorded previously, in its full significance, 

 although many observers of the habits of spiders have 

 noticed this peculiar mode of enfolding the prey in members of 

 the TherididcE. 



Dr. McCook* jusdy remarks, in words to this effect, that 

 Dr. Thorell's system of dividing spiders according to their habits, 

 /.d, mode of providing themselves with the necessities of life, will 

 be interesting to naturalists because it bears upon the correspond- 

 ence between structure and economy, and the value of habit as a 

 factor in classification.-^ 



Now it would seem that either habit produces variation in 

 structure or slight variations in structure give rise at length to 

 peculiar habits, or they both arise simultaneously with mutual 

 influence, and whether the habit has resulted from a modification 

 of the structure, or the structure from the habit, or each acted and 

 reacted upon the other, certain it is that we cannot now (in the 

 case of the spiders at all events) well conceive of, or deal with the 

 one apart from the other, and that, therefore, they must both 

 perforce be taken into consideration in schemes of classification, a 

 conclusion to which Dr. Thorell has long since come. 



So that we would point out that we must not look to habit, 

 per se, nor to structural modification, per se., as valuable factors of 

 classification, but to both regarded as bearing the one upon the 

 other, and our efforts, therefore, should be directed to ascertaining 

 the relations of the one to the other. This is what we have been 

 endeavouring to do by our humble researches recorded above. 

 Hoping that we have been successful in so doing in connection 

 with the tarsal-comb of the T/ierididcB, and that we may be the 

 means of inducing others to take part in this, the most interesting 

 portion of the whole field of natural history exploration, we must 

 close our somewhat incoherent remarks, and refraining from 



* Proc. Acad. Nat. Sci., Philad., 1882, pp. 254 — 7. 

 + The italics are ours. 



