STRUCTURE, FUNCTIONS AND (ECONOMY OF ARANEIDEA. 75 



2. An immature female Thomisus cristatus had the two lateral pairs of 

 eyes only ; the four small intermediate ones were altogether wanting, not the 

 slightest rudiment of them being perceptible even with the aid of a powerful 

 magnifier. 



3. A short but perfectly formed supernumex'ary 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 want- 

 ing in an adult female Epeira inclinata, and the right intermediate eye of the 

 same row was not half the usual size. 



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

 mediate eye of the posterior row. 



Y. The right intermediate eye of the posterior row in an adult female Epeira 

 inclinata had not one-eighth of the natural size, being merely rudimentary. 



The particulars stated in the foregoing cases, which serve to establish the 

 fact, that spiders, in common with many other animals, occasionally 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 important 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 struc- 

 ture, 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 arrangement of their visual organs cer- 

 tainly may be expected to obtain ; consequently, cases 4, 5 and 6, which pre- 

 sent instances of an odd number of eyes disposed irregularly, would be re- 

 garded at all times with suspicion ; as no such objection, however, can be 

 urged against case 1, a solution of the difficulty it presents must be sought 

 for in a more accurate acquaintance with the species. 



Interesting chiefly in a physiological point of view, cases 3 and 7 show that 

 a liability to irregularity in structure is not limited to the eyes, and that 

 those organs are subject to preternatural variations in size as well as number. 



The obscurity in which the cause of these remarkable organic modifications 

 is involved, careful investigation, conducted upon sound philosophical prin- 

 ciples, can alone dispel*. 



Argyroneta aquatica, Dolomedes Jimbriatus, and Lycosa piratica are known 

 to descend spontaneously beneath the surface of water, the time during 

 which they can respire when immersed depending upon the quantity of air 

 confined by the circumambient liquid among the hairs with which they are 

 clothed. There are, however, some spiders of small size, Erigone atra and 

 Savignia frontata, for example, which, though they do not enter water 

 voluntaril}'^, can support life in it for many days, and that without the external 

 supply of air so essential to the existence of Argyroneta aquatica imder 

 similar circumstances. It is probable that this property may contribute to 

 their preservation through the winter, when their hybernacula are liable to 

 be inundated f. 



• Annals and Magazine of Natural History, vol. xi. p. 165-168. 



t Report of the Third Meeting of the British Association for the Advancement of Science, 

 held at Cambridge in 1833, p. 446. 



