r)40 



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 hydrocoel ring still remains unclosed for a long time 

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



Fig. 4:.i.— Stalked larva of Antedon, 

 eighty-four hours old, with twenty-five 

 tentacles, from the right side (after 

 Seeliger). Calcai'eous plates not repre- 

 sented. 1, Right ccelom sac ; '2, stomach 

 intestine; 3, left coeloni sac; 4, saecnli ; 

 .0, vestibule, still closed ; (5, the fifteen 

 primary tentacles ; V, the five pairs ot 

 secondary interradial tentacles ; S, oeso- 

 phagus ; 0, liind-gut; 10, axial organ; 

 11, fibrous strands in the stalk, continua- 

 tions of the axial sinus. 



^ \ ^^^ 



Fig. 402. — Transverse section 

 through the region of the left 

 or oral coslom of an attached 

 larva of Antedon, 108 hours 

 old (after Seeliger). I-V, TJie 

 five radii ; 1, left oral ccelom ; 

 2, oesophagus ; 3, stone caual ; 

 4, parietal canal. 



Fio. 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 ; ha^-lja^, the five basals ; 

 1, right or aboral ccelom ; 2, hind- 

 gut ; 3, axial organ ; 4, parietal 

 ^inus ; 5, ossophagus. 



push tip 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 move being 

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



