IX 



PHYLUM ECHINODERMATA 



385 



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 



FIG. 309. A, view of the under part of a specimen of Asterias rubens. which has been 

 horizontally divided into two nearly equal portions. B, enlarged view of the axial sinus, 

 stone-canal and genital stolon cut across, amb. oss. ambulacral ossicle ; ar,ip. ampullae of the 

 tube-feet ; ax. s. axial sinus ; gon. gonad ; g. stol. genital stolon or axial organ ; marg. marginal 

 ossicle ; nerv. circ. nerve-ring ; oe. cut end of oesophagus ; pst. peristome ; ret. retractor muscle 

 of the stomach ; sept, inter-radial septum ; stone, c. stone-canal ; T. Tiedemann's vesicle ; 

 K. v. r. water- vascular ring-canal. (After MacBride.) 



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 gonads. There is 

 evidence that the sexual cells originate in the aboral end of the 

 axial organ, and travel through the genital rachis and its branches 

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