66 REPORT — 1844. 



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 Epeiridce. 



If the spiders constituting the genus Clubiona 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 investigation still further, if the genera 

 Walckenaera, Theridion, Epeira, Eresus, Salticus, Thomisus, and Philodro- 

 mus be compared together, numerous instances of correspondence in the re- 

 lative 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 

 is 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 thespecific identity of adult spiders of differentsexes, they frequently 

 may be set at rest by placing the spiders together in captivity 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, indeed, 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 di- 

 versity of structure extends to spiders connected by the closest relations of 

 affinity, it is, perhaps, in vain to expect that it will ever be applied with much 

 success to the establishment of genera. 



From remarks on the structure of the palpi to the consideration of the 

 functions they perform the transition is easy and natural. 



Many spiders employ their palpi in assisting to collect the slack line which 

 results from their operations when engaged in ascending the silken filaments 

 by which they have lowered themselves from stations previously occupied, 

 or in drawing in such as have been emitted from the spinners for the purpose 

 of facilitating a change of situation in some other direction. The silk collected 

 on these occasions is formed into a small heap, which is either attached to 

 some fixed object, or is transferred to the maxillae, and, after having been 

 mixed with saliva and reduced in volume by repeated acts of compression, is 

 ultimately allowed to fall to the ground. 



In conjunction with the mandibles, the palpi are employed by females of 

 the species Dolomedes mirabilis and Dolomedesfimbriatusto retain their cocoons 

 under the sternum, in which situation those spiders usually carry them where- 

 ever they move. The LycoscR also avail themselves of the same parts in re- 

 gaining possession of their cocoons when detached from the spinners. 



Certain spiders belonging to the genus Mygale have the inferior part of 

 the tarsi furnished with a dense brush of hair-like papillae for the emission of 

 a viscous secretion, which enables them to ascend bodies having smooth per- 

 pendicular surfaces. Now, as the females of these species usually have the 

 under side of the digital joint of their palpi, which are remarkably long and 

 powerful, supplied in like manner' with papillse, analogy would lead to the 

 conclusion that, in liarmony with their organization and distribution, they also 

 constitute a climbing apparatus. 



Various species of SaUicid^-, to which distinctness and accuracy of vision 



