MEM. M. C. Z., IX. No. 2.— ECHINODERMATA. 17 
PASTE, Vi. 
Development of ASTEROIDEA. Figures from WitHetm Busca and Hvsert Lupwic. 
1-4. Echinaster sepositus. From W. Busch, Beobachtungen iiber Anatomie und Entwickelung einiger Wirbel- 
ul 
2 
oo 
losen Seethiere. Berlin, 1851, Pl. XII. 
. Young pelagic embryo : a, body ; 6 }, so-called brachiolarian appendages. 
. The same embryo somewhat more advanced : a, the body where the future Starfish is developed ; dd, so-called 
brachiolarian appendages ; 0, commencement of a third pair. 
. The young starfish has assumed a pentagonal outline ; the tentacles (b) of the disk are clearly indicated, and 
the brachiolarian appendages have taken their maximum development on each side of the axis a. 
. The most advanced stage of the young Echinaster observed by Krohn. The brachiolarian appendages are 
reduced by resorption to mere rudiments, @ ; b, older pair of tentacles ; d, odd terminal tentacles ; v, young- 
est pairs of tentacles ; f, actinal ambulacral furrow. 
5-49. Asterina gibbosa. From H. Ludwig, Morphologische Studien an Echinodermen, II., 2 Heft, 1882. Zeits. 
f. Wiss. Zool., XXXVII., Pls. I. — VI. 
A,. First ambulacral plate. Ls. Larval esophagus. 
Ay. Second ambulacral plate. Mt. Mesentery. 
Bl. Blood system. Ms. Mesoderm. 
C. — Dorsocentral plate. P. Dorsal pore. 
D. Digestive cavity. 7 El. Right enteroccelum pouch. 
EC. Enterocceelum. T), Tx, Ts, Ts, T;. First to fifth terminal plates. 
Ect. Ectoderm. 1, 2, 3, 4, 5, denote the Hydroceelum lobes and am- 
Eh, Egg membrane. bulacral arm lobes. 
Ent. Entoderm. I, If, (1, IV, V, denote the antiambulacral arm 
Gm. Gastrula mouth. lobes; O denotes the upper side of the embryo 
HC. Hydroecclum. or larva ; U, the lower ; H, the posterior, and 
JRy, JRy, JR3, Ty, TR;. First to fifth interradial. V, the anterior extremity ; Z, left ; R, right; 
Z£l. Left enteroccelum pouch. V L, in front to the left; HU, behind and 
Lm. Larval mouth. below. 
5-10. Stages of segmentation of the first day. 
5. Three spheres of segmentation are shown. I, I, are formed from the division of the upper of the two spheres ; 
II, the lower sphere ; this is originally somewhat larger than the upper sphere. 
6. The lower sphere, II, is now also divided into two, iibieone 
7. The same as fig. 6, so turned as to show the two spheres I,.... 
8. The stage with four spheres somewhat older than the preceding figures. 
9. A stage with eight spheres; I, and II, the two spheres resulting from the division of the spheres I and II 
10. 
11 
12. 
13 
14 
15, 
18 
of the stage of fig. 8. 
Stage with sixteen spheres, which have resulted from the subdivision of the cells I, into I;, and of the cells 
HH, into Ig. 
- Section through a blastula composed of 32 spheres. 
Longitudinal section of a gastrula on the second day. Gm, the gastrula mouth. 
. The same stage, looking into the gastrula mouth. 
- Longitudinal section of an older gastrula, with a decidedly narrower opening, Gm. 
, 16, 17. Posterior, anterior, and right view of an embryo just escaped from the egg, fourth day. 
- Longitudinal section of a gastrula somewhat older than fig. 14 ; the gastrula mouth is approaching the lower 
pole : a, the point at which the diverticula of the gastrula digestive cavity begin to be formed. 
