540 



COMPARATIVE ANATOMY 



CHAP. 



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

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

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



-Li 



d. 



FIG. 451. stalked larva of Antedon, 

 eighty-four hours old, with twenty-five 

 tentacles, from the right side (after 

 Seeliger). Calcareous plates not repre- 

 sented. 1, Right ccelom sac ; 2, stomach 

 intestine ; 3, left coelom sac ; 4, sacculi ; 

 5, vestibule, still closed ; 6, the fifteen 

 primary tentacles ; 7, the five pairs of 

 secondary interradial tentacles ; 8, oeso- 

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

 11, fibrous strands in the stalk, continua- 

 tions of the axial sinus. 



FIG. 45-_'. Transverse section 

 through the region of the left 

 or oral ccelom of an attached 

 larva of Antedon, 108 hours 

 old (after Seeliger). I-V, The 

 five radii ; 1, left oral coelom ; 

 2, oesophagus ; 3, stone canal ; 

 4, parietal canal. 



Fir,. 453. Diagrammatic 

 transverse section through the 

 region of the aboral ccelom in 

 an Antedon larva, 108 hours old 

 (after Seeliger). I-V, The five 

 radii; bi-& g , the five basal.s ; 

 1, right or aboral coelom ; 2, hind- 

 gut ; 3, axial organ ; 4, parietal 

 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. 



