MEM. M. C. Z., IX. No. 2. — ECHINODERMATA 43 
PAACT ET exo Vice 
Development of HototHurorveEa, continued, and Comparison of Ecuinoperm Larvae. Fiqures 
Pp 2 Y 
from Emin SeLenka and JOHANNES MULLER. 
1-13. Cucwmaria doliolum. From E. Selenka, Zur Entwickelung der Holothurien (Holothuria tubulosa und 
Cucumaria doliolum), Ein Beitrag zur Keimblattertheorie, 1876, Pls. XI., XII. Zeits f. Wiss. Zool., XX VII. 
mem Oh ee 
oO 
tee) 
8. 
oy 
10. 
11. 
a. Anal opening. A.  (sophagus. 
61. Blastoderm. B. Stomach from which has separated the vaso- 
ek, Ectoderm. peritoneal vesicle. 
en. Entoderm. H. Stone canal. 
f. . Segmental cavity. N. Nucleus. 
m.  Mesoderm. P. Peritoneal sae. 
m', Outer mesoderm plate. Pr. Right peritoneal sac. 
av! Inner mesoderm plate. Pi. Left peritoneal sac. 
o. Mouth. wu. Original digestive cavity of larva. 
w. Cord of vibratile cilia. V.  Water-system sac. 
x. Water-system pore. Vp. Vasoperitoneal sac. 
. Egg found floating on the surface, in process of segmentation. , germinative vesicle. 
. Completely segmented blastula. s, the part of the blastoderm where the invagination will take place. 
The biastula has become larger. a, position of the future anus ; m, mesoderm cells. 
Gastrula at the end of the second day ; longitudinal section. The migratory cells have accumulated in part 
towards the ectoderm at d, to form later the circular muscular system, and in part remain free in the seg- 
mental cavity. s, the part of the blastoderm where the invagination to form the digestive cavity can be 
traced by the slight depression at that pole. 
Longitudinal section of an older gastrula. 
Sagittal section of larva at the end of the fourth day. 
A!, B!, Cl, show the mode of formation of the water system, and of the two peritoneal sacs as diverticula 
from the original digestive cavity ; 2, the point where the fully formed invaginated cesophagus strikes the 
digestive cavity. 
Free swimming embryo. &, oil globule of the head. 
Section of a larva, about in the stage of fig. 8. Lettering as before, with the following additions : — 
£. Circular vascular ring, with the five oral tentacular vesicles. 
F. The five ambulacral canals. 
G. The ventral ambulacral canal, with two ambulacral tentacles. 
X. Stone canal. 
J. Spheres of food in the stomach. 
K. Anterior lobe of embryo. 
F!. Wall of the peritoneal sac. 
6. Cells with lashes, originating from the vibratile cord. 
+, Polian vesicle. (This is cut off.) 
Older embryo, swimming freely. 
T. The five oral tentacles, which can be nearly entirely contracted. 
G@,. The two ventral ambulacral tentacles, with rudimentary sucking disks. 
€ Oil globule in anterior part of the head. 
Young Cucumaria creeping. The bands of vibratile cilia have disappeared ; the anterior portion of the young 
Cucumaria is rounded, and the oil globule of the interior has been resorbed. D, ventral ambulacral ten- 
tacles, with calcareous sucking disks ; S, calcareous plates of the ectoderm. 
