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MANUAL OF ZOOLOGY 



SECT. 



pear-shaped, thin-walled bladders with long narrow necks, 



which are placed inter-radially. On the sides of the neck 

 of each Polian vesicle (except in the inter-radius containing 

 the madreporic canal, where there is one on one side only) 

 project inwards a pair of little rounded glandular bodies, the 

 racemose vesicles, or Tiedemann's vesicles, the interior of 

 each of which is divided into a number of chambers. 



FIG. 90. Ambulacral system of a starfish, a, ampullae; aj>, Polian vesicles; c, 

 circular canal; m, madreporite; m', madreporic canal; /, tube-feet; r, radial 

 vessels; r', branches to ampullae. (After Gegenbaur.) 



Accompanying the madreporic canal there is an organ, 

 the ovoid gland, the relationships and function of which 

 have given rise to a considerable amount of difference of 

 opinion. It is a fusiform body, the interior of which is 

 divided up into a number of freely communicating spaces. 



