236 Mr. J. BlackM'all on the Structure, Functions 



months of May and June in North Wales. On the 28th of June 

 1840, the third summer of its existence, it underwent its last moult 

 and became adult. Subsequent experiments made with both sexes 

 of this spider tend to corroborate the accuracy of the above con- 

 clu>ion. 



Variations in the colour and size of spiders of the same kind, re- 

 sulting from differences in age, sex, food, climate, and other condi- 

 tions of a less obvious character, as they conduce largely to the in- 

 troduction of fictitious species, have long engaged the attention of 

 arachnologists, while those arising from extraordinary organic modi- 

 fications, in consequence, perhaps, of their less frequent occurrence, 

 have been almost entirely overlooked. The importance which cases 

 of the latter description possess in relation to physiology and syste- 

 matic arrangement will be best illustrated by a few examples. 



1. A supernumerary eye, situated between the two small ones 

 constituting the anterior intermediate pair, has been observed in an 

 adult female TheridionJiUpes. The total number of eyes possessed 

 by this individual was nine and their arrangement symmetrical. 



2. An immature female Thomisus cristaiiis had the two lateral 

 pairs of eyes only ; tlie four small intermediate ones were altogether 

 M'anting, not the slightest rudiment of them being perceptible even 

 with the aid of a powerful magnifier. 



3. A short but perfectly formed supernumerary tarsus, connected 

 with the base of the tarsal joint of the right posterior leg on its outer 

 side, has been noticed in an adult female Lycosa campestris, 



4. Deficiency of the right intermediate eye of the anterior row 

 has been remarked in an adult male Lycosa cambrica. 



5. The left intermediate eye of the posterior row was perceived to 

 be wanting in an adult female Ep'eira mclinata, and the right inter- 

 mediate eye of the same row was not half the usual size. 



6. An adult female Ciniflo atrox was found to be without the left 

 intermediate eye of the posterior row. 



7. The right intermediate eye of the posterior row in an adult fe- 

 male Ep'eira incUnata had not one-eighth of the natural size, being 

 merely rudimentary. 



The particulars stated in the foregoing cases, which serve to esta- 

 blish the fact, that spiders, in common with many other animals, oc- 

 casionally exhibit instances of anomalous structure, derive no small 

 degree of interest from their novelty ; but when it is borne in mind 

 that all the examples except one have reference to those impoi'tant 

 organs the eyes, important, not only as regards the function they 

 perform, but also on account of the extensive use made of them in 

 the classification of the Araneidea. that interest becomes greatly 

 augmented. 



As spiders with four eyes have not yet been found, it is a matter 

 of some consequence to caution observers against mistaking a mere 

 defect in structure, like that recorded in case 2, for such a discovery. 

 Whether there are species provided with an odd number of eyes or 

 not is at present conjectural ; should such exist, symmetry in the ar- 

 rangement of their visual organs certainly may be expected to ob- 



