378 



ZOOLOGY 



SECT. 



coverings which they may derive, according to their situation, 

 either from the external epidermis or the internal ccelomic epi- 

 thelium. The muscular layer is most strongly developed on the 

 tube-feet, where it consists of two strata, and is also well developed 

 on the ampullae and Polian vesicles. 



The stone-canal is enfolded in the wall of a wider canal, the 

 axial sinus (Fig. 314, ax. s), which forms a part of the perihaemal 

 system already referjed to. The axial sinus runs nearly vertically. 

 At^its oral end it opens into the internal division of the oral ring 

 sinus ; aborally it approaches close to, if it does not actually open 

 into, an aboral ring sinus : it also communicates aborally with the 

 stone-canal, and opens on the exterior through certain of the pores 

 in the madreporite. 



card.st 



asnp 



FIGGIS. Anthenea flavescens. Latera view of a dissection in which one of the rays and 

 a portion of a second have been removed, and in which the alimentary canal has been laid 

 open. amp. ampullae ; an. anus ; card. st. cardiac pouch of the stomach ; int. ccec. intestinal 

 Ciecum ; ip. inter-radial partition ; mad. madreporite ; mad. can. madreporic canal ; OP. 

 ovary ; pi/I. ccec. pyloric caeca ; r. cut ends of the ring-vessel of the ambulacra! system ; 

 ring v. position of the ring-vessel ; retr. retractor muscle of cardiac pouch of stomach ; 

 s. cavity of the stomach. 



Accompanying the madreporic canal and also enfolded in the wall 

 of the axial sinus there is an organ the axial organ (Fig. 314, 

 g. stol) -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 assumes an appearance of com- 

 plexity largely due to both its inner surface (i:e., that turned 

 towards the axial sinus) and its outer (that facing the ccelome) 

 being folded in a complicated manner. The axial organ contains 

 strands of lacunar tissue, i.e. of the same tissue that composes the 

 so-called haemal system, and is intimately related with the 

 latter. Its essential morphological character, however, appears to 

 be that of a genital stolon. At its aboral end it is continuous with 

 a genital rachis, which, in the form of a ring, runs in the aboral 

 perihsemal sinus, and gives off branches to the gouads. There is 



