-200 



ixve[!T,:beate animals. 



Uills tlirough the body, and lias iKitliiiig to do with the propulsion of 

 the non-aerated or venous blood through the gills. There is never 

 any distinet head in any of the Bivalves, and for this reason they 

 are snnietinies called the "headless" (/irfpluthnis) Molluscs. The 

 mouth is simply placed at the anterior end of the body, and is never 

 furnished Avith teeth, though usnally provideil with membranous 

 lirocesses or "palpi" (tig. 139, Iji). The mouth opeu.s into a g\dlet 



niiuTii;itfcif'|iTfs.'!itatiiiu (if Ihr anatomy of fi Rijihon- 

 II. I I.'M iiiautl.'-l.ili.- arc r.-iii.iVL'.I, ami tlie siplions 

 .f Carti[a'j;i'-iiit ; .j ^[.iulh; //. Labial palpi; ft 

 : .s/ Sao I'.nitainiui,^ flip crystalltno stylet : t I In- 

 (/.): r Rrotnni, toriiiinalin;,^ in tlie anus; ft.7 An- 

 iililiiot.ir ; )! Supr3<i'soiilia;.;oal or c^TOliral yan^'liun 

 [ njiuar.is, sr. that the ganglion comes to lie below 

 I): ;(■ rari.'i.i-s]ilanclinic or branchial f,':uifjlion ; 

 liu'lit niantl.'-l.ib.- ; rs R.'trai-tor mnscle of the 

 lift M.l.' : .; R.aial organ (" Organ of Bojanns"); 

 sipb.ii]. 



yhi<;h cindncts t.> a .st.imach. The intestine i.s convoluted, and 

 UHu;dly perf.irates tli.' veii(ri.-le of the heart, ultimately terminating 

 in a distinct .-inus, w hich is a,Kya,ys placed near the re.s])iratory aper- 

 tui-e (tig. i:'.!l,/'). A Lirg.. iinil \vi-ll-ileyelci]jed lixer is ;d,so jiresent. 



The Jiervous system h;is ils normal form of three principal masses 

 —the cerehr.il, tli.' p.'ild, ;inil the ]iarieto-splancliuic ganglia. 



Til.' iiuij.irity .if llic ]!i\.-ihe i\l..Ihises liave the sexes distinct, but 

 th.'V an: ; .iinctim,; ; united in the saiue individuid. The young are 



