MEM. M. C. Z., IX. No. 2.— ECHINODERMATA. 21 
36. Embryo in which the larval organs, a @, are forming. 
87. Somewhat older embryo. 
88. The young Starfish is well advanced: ¢, ambulacral tentacles; the brachiolarian appendages, aa, are fully 
developed, and a small tubercle, 6, has formed on the upper surface of the larval organ. Seen from the 
actinal side. 
39. The same as fig. 38, seen from the abactinal side. 
40. Somewhat older stage, seen from the actinal side : the young Starfish has now assumed a well-defined pentago- 
nal outline. 
41. The same embryo as fig. 40, seen from the abactinal side. 
42. The same embryo, about two months old, seen from the abactinal side after the resorption of the larval organs. 
43-46. Echinaster Sarsii. From J. Miiller, Ueber den Allgemeinen Plan in der Entwickelung der Echinoder- 
men (Pt. 6), 1852, Pl. I. Abhandl. der K. Akad. der Wiss. Berlin, 1853. 
a. Larval organ, odd brachiolarian arm. f. Interior cavity. 
b. Larval organ, paired brachiolarian arms. f!. Cavity leading to the brachiolar appendages. 
c. Tubercle between the brachiolarian arms. g. Digestive cavity. 
d. Cortical layer. h. Interior of the digestive cavity. 
e. Inner layer. z. Tentacles of the Starfish. 
43. Longitudinal section through an embryo. 
44. Transversely longitudinal section across the brachiolarian arms. 
45. Longitudinal sections of an older embryo in which the body cavity is divided into two, one of which contains 
the digestive cavity, and the other communicates with the larval organs. 
46. A similar section through an embryo somewhat older than fig. 45. 
47, 48. Wurmformige Asteric. From J. Miiller, Ueber den Allgemeinen Plan in der Entwickelung der Echino- 
: dermen (Pt. 6), 1852, Pl. I. Quoted above. 
a. Lateral ambulacral tentacles. b. Odd terminal tentacle. c. Spines of the actinal surface. 
47. Wurmférmige Asteric, seen from the abactinal side. 
48. The same, seen from the actinal side. 
49-51. Pteraster militaris. From J. Koren and D. C. Danielssen, Observations sur le Développement des Asté- 
ries, in Fauna littoralis Norvegie, Seconde Livraison, 1856, Pl. VIII. 
a. Anal opening. d. Circular water canal. 
6. Intestinal canal. e. Madreporic canal. 
c. Extremity of the intestinal canal. 
49. Young embryo. 
50. Young embryo which has assumed a pentagonal outline. 
51. A young Starfish seen from the actinal side ; +, ambulacral plates ; c, tentacles. 
Figs. 49, 50 are much younger than the stages figured by Sars ; see this Plate, figs. 20-23. Fig. 51 is about 
in the stage of fig. 22. 
