IG rUN«TH)N '»»• |>l<;»>TION. 



the |»ii«!Uini' i>f the ranal, whirh it rl.*r?» In i>n-\ ( nt thi* l>orkwiinl nionnx tit of thr digrslcd 

 maif*. Thi> »<*f;iit(<nt rt*r<>gnlzr<i n» tln' ciituih is ^h<•rt, niui in diirrt rumniuiiirtilion }^Hh 

 the a»l»Ti<>r tiiJm ; but in soiin" cnM-n it trvmi m if Juinvd latrmlljr to it,nn<l thrn it liuft the 

 aplM'rtnmc.' of a |x.ui-h. Klui"!-* an- Mjpix-Mtl t-. Iw iMTrPl«-<l I'j warty fXrr«*r«n«* vitiialnl 

 0|>«)n the inur.<U!» face of tlii.H int<<>linr. «l«siKin<l t<> aid in the •lip«->*tivr pror*-**. 



Tht' rrrtuni i^ tliat |>Jtrt of t)ie larp- iiit(>tiiii-!t whirh ti nninatiit thr ulinirnlary runal 

 boluw : II isalwa>!t !«h<irt, ami i.s ^urni^ll*-«i with a s]>hinct< r nt ilit ciln tmly. It ifl niit^- 

 oular, has thirlirr walls than tin- raruni, umi n'v«!« ►hajK- ami f'-rni t«. thr txtn imnig. 



The funrtit'U «>f dinivttit'n niiuin .«*, in adtlitiou to Iht* I'urnial tuix- llin u^h whuh thr 

 part'ut matter must jiiuw, a suppl* uf rtrrtakn fluids which fthall imjakw a M>lvfnt |>(>wer 

 upun the riintaim"*! masa ; and hi'TP than one kind nf fluid swnr* t«> U- neres-ar). Though 

 thc«c dinVn-nl tlui«U ann-*- in use ami fflixl willi analoRoiLs ones fauid in the higher ani 

 mmls, tlie organ"* which M'<-r»-te them have a very diflt-rent form : indeed, the diflerincf is 

 •o gn'ut, tliat a student wh"'S«' view.sof the fuiielionof digotion have Jieen ohtainetl s<dclj 

 from the oKsirvation of (he on;ans of a vertebrate animal would not at fiist rrognize the 

 parts which |H'rforni similar functions in insfcts. 



The Sfcretory organs, and those wliich are 8ul»servl< nt to digtslion, are alwa\s tubular 

 la Insects : the gland or imn-m-liyma present in quadruiNds U-ing entini) alis^nt in In- 

 wots, these organs are reilm^-d t-» their simplest form. The kinds of tuUs laking their 

 names acconling to the nature of the fluid s<'creted, arv the ntlimry, LUiury, and urinary. 

 The salivary apjmratus is quite C'liii'Iicated : it cimsists of tulies, single and double, and 

 oven tri|>le, sjtuatid arouml the eM^.liiigiis and nu'iith, autl provide«l with Imgs that serve 

 as reservoirs. The tuU^soi>en into the niouth oresophagtis by two..r more e\er»i<>ry orifices. 

 The salivary api>anitus is most jH'rfect in the haustellata or sucking insects ; the tubes 

 ••(Mending into the abovenametl cavities in a meandering course, whenby the extent of 

 ■eoreting surface is much increasid. 



The operation of salivation is an imix.rtant prelimiiwry to digestion : mi\«tl with the 

 fuotl, the sjiliva serves tos-ifttn its consistence, while it al.x) carries along with it much air 

 which apjHjip* to U' necessjiry for some pur]>oM- in the economy. The l>ile is a still more 

 imiMirtant fluid than the saliva : it is s«-cn<l»ul in longcaj>illary liiUs, more or li-s< flexuusc 

 and fohbHl uj>on thenis<-lves, which connect with the alimentary tulu- Ixdow the stoniarh, 

 or just Ix'hind the pylorus ; though they S4^>metimes continue further down, and enter near 

 Iho ca«cum. These tul>es var)' in nuinl)er : there are usually two, especially in c<deopteni, 

 bemiptera and diptcra ; but in these onlers they are not al stdulely iiniA rm, us in the 

 oerambycid.e then- are three, and four in S4.me diptera, while in neiiM'plera there are six, 

 and in certain neun>|>terons gnaips as many as eight. Where the nundi-r of the tuU< 

 varies, however, it o|»trates as a comixnsjition for their length : for exatii]>le, if the simple 

 tnbes arc each five or six times the length of the body, their numU-r is les< ; but when 



