332 OBSERVATIONS ON THE 
but also on account of the” extensive use made of 
them in the classification of the Arancidea), that in- 
terest becomes greatly augmented. 
As spiders with four eyes have not yet been found, 
though such there very probably may be, it ista mat- 
ter of some consequence to caution observers against 
mistaking a mere defect in structure, like that re- 
corded in case 1, for such a discovery. In the case 
of the spider numbered 2, the symmetrical disposi- 
tion of the organs of vision might induce an inexpe- 
rienced arachnologist not only to assign to it a place 
in the tribe Senoculina, but also to propose a new 
genus for its reception, although its appropriate 
situation in a systematic arrangement of the Aranei- 
dea is plainly indicated by its other characteristics of 
structure and economy. 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 certainly may 
be expected to obtain; consequently, cases 3, 4, and 
5, which present instances of an odd number of eyes 
disposed irregularly, would be regarded at all times 
with suspicion: as no such objection, however, can 
be urged against case 6, a solution of the difficulty it 
presents must be sought for in an accurate acquaint- 
ance with the species. 
Interesting chiefly in a physiological point of view, 
cases 7, 8, and 9 show that a liability to irregularity 
