378 



ZOOLOGY 



SECT. 



coverings which they may derive, according to their situation, 

 either from the external epidermis or the internal coelomic 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 referred 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 ^f^^,^ ' " i 



ip 7?i<zj[ . can 



EiG."31 5. 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. ampulla) ; an. anus ; card. st. cardiac pouch of the stomach ; int. coec. intestinal 

 caecum ; ip. inter-radial partition ; mad. madreporite ; mad. can. madreporic canal ; ov. 

 ovary ; pyl. ccec. pyloric caeca ; r. cut ends of the ring-vessel of the ambulacral 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 

 perihaemal sinus, and gives off branches to the gonads. There is 



