and (Economy of the Araneidea. 225 



palpi of spiders to which their diversified structure and important 

 functions undoubtedly entitle them. 



Much difference is observable in the relative proportions of the 

 several joints of the palpi of female spiders, not only in species con- 

 stituting the same family, but even in those belonging to the same 

 genus ; while, on the other hand, it frequently happens that females 

 belonging to different genera bear a striking resemblance to each 

 other in this particular. It is among male spiders, however, that 

 these peculiarities are the most marked, and to them may be added 

 structural differences and resemblances both of the palpi and sexual 

 organs still more conspicuous. 



A great similarity in the form of the organs of reproduction, in the 

 simplicity of their structure, and in the manner of their connexion 

 with the digital joint of the palpi, which has no cavity opening ex- 

 ternally, may be seen in certain males of the family Dysderidce, ; in 

 Dysdera erythrina^ Dysdera Hombergii, Segestria perjida^ Segestria 

 senoculata, and Oonops pulcher^ for example ; and this similitude is 

 extended to the males of various species belonging to the family 

 Mygalidce. 



Between the males of Pachygnatha Clerchii and Tetragnatha ex- 

 tensa there is a near approximation in the structure of the palpi and 

 sexual organs, yet these spiders are not included in the same family, 

 the former belonging to the Theridiidce, and the latter to the Epei- 

 ridce. 



If the spiders constituting the genus Cluhiona be compared with 

 those of the genus Drassus, and those of the genus Linyphia with the 

 species comprised in the genus Neriene ; or, extending the investiga- 

 tion still further, if the genera Walckenaera, Theridion, JSpeira, Ere- 

 sus, Salticus, Thomisus, and Philodromus be compared together, 

 numerous instances of correspondence in the relative proportions of 

 the joints of the palpi will be perceived immediately ; at the same 

 time, striking contrasts will present themselves to the eye of the 

 observer, not as regards proportion alone, but organization also, even 

 among nearly allied species. 



As the full development of the palpi and the organs of generation 

 connected with them indicates a state of maturity in male spiders, the 

 skilful arachnologist }^ enabled, by attending to this circumstance, 

 not only to distinguish adult males from females, but likewise from 

 immature individuals of both sexes. This knowledge is useful in 

 preventing him from falling into the too common error of mistaking 

 young spiders for old ones, and of describing them, and the sexes 

 of spiders of the same kind, as distinct species. When any doubts 

 exist as to the specific identity of adult spiders of different sexes, they 

 frequently may be set at rest by placing the spiders together in cap- 

 tivity and noticing whether they pair or not. 



The great diversity of structure observable in the palpi and sexual 

 organs of male spiders supplies excellent specific characters, and, in- 

 deed, frequently presents the only available means of distinguishing 

 species of similar colours and dimensions from each other ; but when 

 it is borne in mind that this diversity of structure extends to spiders 



