Redundant Organization among the Araneidea. 167 



posterior row was not one-eighth of the natural size,, being 

 merely rudimentary. 



The particulars detailed 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 refer- 

 ence 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. 



Spiders with six and eight eyes have long been known to 

 arachnologists, and Mr. MacLeay has recently published an 

 account of one or two species discovered by him having two 

 eyes only*. That spiders possessing four eyes will be found 

 at a future period, when this neglected branch of natural sci- 

 ence shall be more extensively and zealously cultivated than it 

 has yet been, is highly probable ; it becomes a matter of some 

 consequence, therefore, to caution observers against mistaking 

 a mere defect in structure, like that recorded in case 2, for 

 such a discovery. Had the female Thomisus cristatus, in 

 which that defect was noticed, been an undescribed species, 

 and the only individual obtained, not a new genus alone, but a 

 new family and tribe also would probably have been proposed 

 for its reception f. 



Whether there are spiders provided with an odd number of 

 eyes or not is a more doubtful conjecture ; should such exist, 

 symmetry in the arrangement of their visual organs certainly 

 may be expected to obtain ; consequently, cases 4, 5 and (>, 

 which present instances of an odd number of eyes disposed 

 irregularly, would be regarded at all times with suspicion. 

 Against case 1, however, no such objection can be urged ; and 

 as the spider there introduced to notice was undescribed when 

 captured by me, I should have felt much perplexity in assign- 

 ing it a place among the Araneidea, had I not been so fortu- 

 nate as to procure other specimens of it at the same time. 



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 pre- 

 ternatural variations in size as well as number. 



I shall not attempt to speculate upon the cause of the or- 

 ganic modifications which form the subject of this article ; to 



* Annals and Magazine of Natural History, vol. ii. pp. 3, 4. 



f The difference in the number of eyes with which spiders are provided 

 has been proposed as the basis of their distribution into tribes. Transactions 

 of the Linnaean Society, vol. xviii. p. 602. 



