110 



INVEHTEBliATE ANIMALS. 



(fig. 68). It opens into a long convoluted digestive tube, which is 

 attached to the body-walls bj' a delicate mesentery, and terminates 

 in a large muscular chamber or "cloaca" (fig. 6!J), which in turn 

 comnmnicates with the exterior liy the anal aperture. Springing 

 from the cloaca in many Holothurians are two much-branched tubes. 



us. — CuGunutria frriii<!iis'i 

 slinwin,^ the crown 'il' IrnllnTy 

 tfiiLiclcs round tin' iimntl 

 iUKl tJie rows of 1 iiltc.ri.ct. 



tin, — Hidothuniidea. Sciiii-diagi-aiuniatic 

 loii;:itii(iiTial ML'ction of a Holotlmriaii. t 

 ']'iiil:iclr.s ; ,■ Calcareous ring at tlie base of 

 (lie fcnlaclcs ; p Polian vesicle; s -Santl- 

 faii'il; til Alimentary canal; <J Duct of 



I tie reproductive organs; c^ Cloaca; a Anus ; 



I I Res])iratory tree. 



which run forward towards the anterior end of the body, and which 

 .'ire tilled with sea-water from the exterior. These tubes seemingly 

 .'ict as respiratory organs, and are usuallj' spoken of as the " re.sjiira- 

 tory tree " (fig. 69, / /). The ITolothurians have a nearly world-wide 

 distribution, and are fouml from between tide-marks up to great 



