540 



COMPARATIVE ANATOMY 



wliose floor it lies after as before the process. It has passed from the horse-shoe 

 shape to tlie circiihir, but the hydroccel ring still remains unclosed for a long time 

 at the point where the gape of the horse-shoo formerly was. Its five outgrowths 



X- 

 2- 





Fio. 4r)l.— Stalked larva of Antedon, 

 eighty-four houi-s old, with twinty-iivi- 

 tentacles, from the right side (after 

 Seellger). Calcareous jilates not repre- 

 sented. 1, Right coeloni sac ; 2, stomach 

 intestine ; 3, left cceloni sac ; 4, sacciili ; 

 5, vestibule, still closed ; 6, the fifteen 

 primary tentacles ; 7, the five pairs of 

 secondary interradial tentacles ; S, ceso- 

 pliagus ; 9, hind-gut ; 10, axial organ ; 

 11, fibrous strands in the stalk, continua- 

 tions of the axial sinus. 



Fiii. 4.'.J.— Transverse section 

 through the region of the left 

 or oral cceloni of an attached 

 larva of Antedon, 108 hours 

 old (after Seellger). 1-V, The 

 five radii ; 1, left oral cielom ; 

 •2, o-sophagus ; 3, .stone canal ; 

 i, parietal canal. 



Fin. 453. — Diagrammatic 

 transverse section through the 

 region of the aboi'al coelom in 

 an Antedon larva, 108 hours old 

 (after Seellger). I-V, The five 

 radii; hai-hug, the five basals ; 

 1, right or aboral c(elom ; '2, hind- 

 gut ; 3, axial organ ; 4, paiietal 

 sinus ; 5, oesophagus. 



push up the ectoderm of the floor of the vestibule into the vestibular cavity ; they 

 soon appear to be trilobate, so that in all 5 x 3 tentacles are present, ten more being 

 added to them, which arise in pairs at the bases of the primary outgrowths. 



