Plate XX. 



Asterias pallida (Ag.). 



All the figures in this plate are magnified GO diameters. 



17. A series of frontal sections of a specimen in stage D. The sections are each 

 0-7 IX thick, and are represented as seen from the ventral side, a is the 16th, 

 h the 37th, c the 50th, d the G6th, and e the 83rd section from the most ventral 

 section, there being 120 sections in all. 



18. A series of frontal sections of the specimen represented in Fig. 13. The shrink- 

 age is due solely to the usual procedure of imbedding. The sections are eaeh 

 6-7 [X thick and are represented as seen from the ventral side. There are 7 

 sections between a and h, 11 between /; and c, 12 between c and (/, 11 between 

 (/ and e, and 5 between t' and /. 



ABBREVIATIONS. 



an. pro protoproct. 



bi-ach. d right brachiolaria arm. 



,, med median „ ,, 



s left 



cm. aq pore canal. 



can. aren stone canal. 



cav. perihsem iierihsemal cavity. 



ent'c'l. a anterior ente rocœl. 



,, cir circular ,, 



„ epigas epigastric ,, 



,, p. d right posterior enterocœl. 



,, p. s left ,, „ 



„ p'. s' secondary left posterior enterocœl. 



„ periœs periœsophageal enterocœl. 



gast stomach. 



int- intestine. 



sin. ax axial sinus. 



sin', ax' closed portion of the axial sinus. 



tent. dor. a anterior dorsal tentacle (= bipinnaria arm.) 



„ „ p posterior ,, 



,, med. a anterior median ,, 



„ ,, p posterior „ ,, 



„ ven. a anterior ventral ,, 



,, ,, p posterior ,, ,, 



vas. aq. cir circular water-vascular canal. 



,. „ rad radial 



