Plate XXI. 



Asterias pallida (Ag.). 



In the case of transverse sections they are représente! as seen from the pos- 

 terior pole. 



19. Dorsal median portion of a cross section from stage C, through the level of the 



dorsal pore, x 395. 

 '20. Ditto a little in front of the preceding, x 395. 



■21. Part of a transverse section from a stage somewhat prior to stage B (stage A), 

 through the level of the inner opening of the pore-canal, x 250. 



22. Eight half of a transverse section from stage B, 8 sections (each=G-7 fi. ) behind 

 the dorsal pore, x 250. 



23. Dorsal portion of a transverse section from a stage a little prior to stage C, 

 through the pore-canal. x 250. 



'24. A transverse section from stage C, through the posterior part of the hydro- 



cœl. x86. 

 "25. Dorso-dextral portion of a transverse section from stage C, 15 sections (each 



=^6-7 ji ) behind the dorsal pore. x 390. 

 ".20. Diagrammatic representation of the separation of tlie inner openings of the 



pore-canal and stone-canal, as seen from within the left anterior enterocœl. 



27. Muscular fibrils in the peritoneal epithelium of larva, a from the anterior eu- 

 treiuity of tlie enterocœl, }> from the region about the stomach, x 395. 



28. A small portion of a radial section, next the metastome, from a stage a little 

 prior to stage H. a plate of cells connecting the circular hydrocœl with the 

 anterior enterocœl. 



"29. Portion of a radial section from a stage about the same as stage H. x 395. 



ABBKEVIATIOXS. 



au. jjro protoproct. 



br.Tch. d right bmchiularia arm. 



„ med median ,, „ 



s left 



■can. aq. pore canal. 



can. aren stone canal. 



•cav. peribœm. ... perihœmal cavity. 



-enfc'c'l. a anterior enterocœl. 



cir circulnr ,, 



epigas.... epigastric 



,, p. d right posterior enterocœl. 



p. s left ,, 



„ p'. s' secondary left posterior en- 

 terocœl. 



.,, periœ-.... periœsophagt-al. 



gast stomach. 



int intestine. 



sin. ax axial sinus. 



sin', ax' closed portion of the axiil 



sinus. 



tent. dor. a anterior dorsal tentacle ( = 



bipinnaria arm.) 



„ ,, p posterior dorsal tentacle. 



,, med. a. ... anterior median ,, 

 ,, ,, p. ... posterior ,, ,, 



,, ven. a. ... anterior ventral „ 

 „ „ p. ... posterior ,, 



vas. aq. cir circular water-vascular cana 



„ „ rad radial „ 



