It ri'NCTION 0» VISION. 



hnvi' nrrivitl thf naiunt of orrlli nnd ilrmmata, rihI urr gfuernlly thrw in nurnltcr, and 

 ■muiar*! in l)u< form <»f a irlaimlf ; hut thrrr may Iw but lwo,iir only one. Tlielr structure 

 quallfli-^ fh«m for vU'wIuk «irh i>l>Jrct» only iw nrv c\<r*e at hnml. 



The c»ni|>oun»l «•>»• |>r«-«<-nM u n-tirulnlrd njiiK-amiirr un<l«-r tin- uiicnFSfr.j* : the surface 

 i* omvex or glohulnr ; hut t)ir organ It imniovahh-, cxopt hy tin- motion of the head. 

 The reticuliilril apiH-uninrr i> pnxlured l>y tlie line* tliut mark ihr U>unclary of tnch e)c 

 or len-H : these are hexai;oiutl,ai>tl tlu-ir numl>er isuhuo^t inrrwllhly Rreat in some sj>ecie5. 

 They vary in tl»h» n-.«|KTt fn.m 50 In the ant, to 2S,000 in a species of Mvrdtlln : the 

 bulterlly h.i.>« 17,00(1, ami the iln»K>>nfly 12.511. Each eye is furnlMied with an a]>paratu8 

 •mlliiiiiitly iK-rfict for tin- exrrris- of vi<.ii»n in its uplien- : it has its len.* for refraction, 

 its chon>i<l for tile corn-rtioH of ni>ernition, and it> retina lor the reception ..f the imaRefl 

 of exteriwl objects. Ijich >ini?le eye, however, must embrace an extremely limited flehl of 

 vision, and tliere is mo iloubt that it re<juires the us<' of many of these eyes to see a Mngle 

 object ; for only thow rays of light that fall i>erixiidiculurly uin.n the eye can reach the 

 optic nerve. 



The eyes of pre<hieooU8 insects, such as the lirunonlly, are large, prominent and globular: 

 hence they enjoy, altogether, a large field of vision. In those insects, on the other hajid, 

 which an' contliied in tluir range, or are jiarasitic, the field of view is diminished by ■ 

 rt'VerM' of circumstiinces. 



The nerve of each eye tenninates in n common nerve : this n»u.st !>«> regnnletl as the 

 sensonum cofiununf, the nervoUS jdane UjHai which the image of an object is spread. Some- 

 times the eve is iHMlunculated, or place«l uiM>n a f<x>tst4ilk : sometimes it Is Miuicircuiar, 

 In c.>ns«-qucnce of the iniidantutiou of the anteimu*, and Indeed this implantation may be 

 »uch as to give the semblance of four eyes. In other instances the size of the eye is a sexual 

 mark. 



We are too much in the hid>it of l.«>king vaguely upon the in.s«ct trilx-s. While we 

 recognize the movements.. f the vertel>iute<l class a.s resulting fmm distinct acts of the will, 

 and as coiitndled I'y internal feelings, we are little disjH.s^d to entertain the view tliat the 

 api>aratus of a fly or a iw-etle indicates similar interiuil motivts for action ; of, in other 

 wonLs, we do not i>oss«'SS .S4» liMly a seiLse of the iK-rfection of the U'ing of the in.sect, as 

 of the Iteing of the higher onler. We see, however, that Insects have eyes to see, ears to 

 hear, and organs of smell ; a highly develoi>cd nervous apparatus, and an active circula- 

 tion : in fine, the ins»-ct moves in n world of its own. which takes no part in the .<i>here 

 beb)nging t<> the mollu.sca or vertebrata. Its s«-ns«-s and organs of nninial life, how t-ver. give 

 It a wide sphere of activity, and have prepare<l It f-.r fulfilliim imjH.rtant functions, and 

 furni-ihed It with n cajMibility to aflfect very matt rially the interests i.f man. lUwn widely 

 diffus»'d,and their life overflowing with activity, alwajs moving as if ini|Hll<d forward l>y 

 Important busings or engaged in errands of the most momentous character, they seem to 



