THE SENSES AND THEIR ORGANS. 



317 



with the fingers near the apex of the abdomeia, he moved his abdomen up 

 and down, and its base or the serrated valve near the base of the thorax 

 was rubbed upon. The female of the species does not possess these or- 



Mr. F. Maule Campbell - has taken up these observations of Westring, 



and in a valuable and interesting paper added much to our information. 



He made special studies, both of the male and female of Stea- 



Stridula- ^^gda guttata and Steatoda biiiunctata. In the fore extremitv of 



"j? j^^ the abdomen he found, in the male of Guttata, that the socket 

 ridioids. , . . ' , . . , . 



is a complete ring with some strong chitmous spurs on the in- 

 side of its external edge (Fig. 299), which is also roughly serrated. That 

 of the female is divided into two parts, the inferior being smallest, while 

 the superior, as in the male, is the deepest. In the female (Fig. 298) 

 there are no spurs. The inner edge, however, is undulated, and in points 

 becomes angulated, while a little below are stiff hairs on small protuber- 

 ances. The chitinous tlioracic exten.sion of the male is marked on its 



Pig. 298. 



Fig. 299. 



Fig. 300. 



The stridulating organs of Steatoda guttata, male and female. (After Campbell.) 

 Fig. 298. Female ; view from above, of chitinous ring or socket attached to abdo- 

 men, covering the union with thorax. Fig. 299. The same part of the male. 

 Fig. 300. View from above of chitinous extension of thorax of female. 



superior surface with many tine, parallel, transverse grooves, which are 

 absent in the female. (Fig. 300.) In the same position on both sexes are 

 several ridges which are less numerous in the male. Thus, it appears 

 that while it is likely that individuals may vary in details, the female of 

 Steatoda guttata has organs adapted to stridulation, as well as the male. 



Mr. Campbell also examined both sexes of Steatoda bipunctata, and 

 found that the socket of the male is much shallower than those of the 

 male and female of Guttata. The inside of the external edge is rough, 

 and the sides are lined with a row of bristles seated on prominences. The 

 only opf)osing surface is a spinate ridge on the base of the thorax, which 



' Since. this original discovery Westring liad heard many males of Theridium and Stea- 

 toda stridulating. Among these he mentions Theridium c-astaneum Clerck, Tlieridium (Stea- 

 toda) liiinmctatum (page 1S.5), Theridium liammatum, Theridium albumacnlatum (page 186), 

 Tlieridium (Steatodns) guttatum (page 18S). 



^ On Supjiosed Stridulating Organs of Steatoda guttata and Linypliia tcnebricola, Linn. 

 Soc. ,I<iur. Z(i(,l., Vol. XV., ISSO, page 152. 



