270 THE DESCENT OP MAN. 



"voured, a sight which, as he adds, filled him with horror and 

 indignation.""' The Rev. O. P. Cambridge"^ accounts in the fol- 

 lowing manner for the extreme smallness of the male in the 

 genus Nephila. "M. Vinson gives a graphic account of the agile 

 "way in which the diminutive male escapes from the ferocity of 

 "the female, by gliding about and playing hide and seek over her 

 "body and along her gigantic limbs: in such a pursuit it is evi- 

 "dent that the chances of escape would be in favor of the smallest 

 "males while the larger ones would fall early victims; thus grad- 

 "ually a diminutive race of males would be selected, until at last 

 "they would dwindle to the smallest possible size compatible with 

 "the exercise of their generative functions, — in fact probably to 

 ' the size we now see them, i.e., so small as to be a sort of para- 

 "site upon the female, and either beneath her notice, or too agile 

 "und too small for her to catch without great difficulty." 



Westring has made the interesting discovery that the males 

 of several species of Theridion== have the power of making a 

 strldulating sound, whilst the females are mute. The apparatus 

 consists of a serrated ridge 8,t the base of the abdomen, against 

 which the hard hinder part of the thorax is rubbed; and of this 

 structure not a trace can be detected in the females. It deserves 

 notice that several writers, including the well-known araohnolo- 

 gist Walckenaer, have declared that spiders are attracted by 

 music."' Prom the analogy of the Orthoptera and Homoptera, 

 to be described in the next chapter, we may feel almost sure 

 that the stridulation serves as Westring also believes, to call or to 

 excite the female; and this is the first case known to me in the as- 

 cending scale of the animal kingdom of sounds emitted for this 

 purpose."^ 



Class, Myriapoda. — In neither of the two orders in this class, 

 the millipedes and centipedes, can I find any well-marked In- 

 stances of such sexual differences as more particularly concern 

 us. In Glomerls llmbata, however, and perhaps in some few 

 other species, the males differ slightly in color from the females; 

 but this Glomeris is a highly variable species. In the males of 



21 Kirby and Spence, 'Introduction to Entomology," vol. i. 1818, p. 280. 



"2 'Proc. Zoolog. Soc.,' 1871, p. 621. 



"^Theridion (Asagena, Sund.) serratipes, 4-punctatum et guttatum; 

 see Westring-, in Kroyer, 'Naturhist. Tidskrift,' vol. iv. 1842-1843, p. 349; 

 and vol. ii. 1846-1849, p. 342. See, also, for other species, 'Araneae 

 Suecicae,' p. 184. 



" Dr. H. H. van Zouteveen, in his Dutch translation of this work 

 (vol. i. p. 444), has collected several cases. 



25 Hilgendorf, however, has lately called attention to an analogous 

 structure in some of the higher crustaceans, which seems adapted to 

 produce sound; see 'Zoological Record,' 1869, p. 603. 



