MEM. M. C. Z., IX. No. 2.— ECHINODERMATA. 1d 
Bian LV. 
Development of OpHiurotpEa, continued. Figures from Nicouas Caristo Apostotipks and 
JOHANNES MULLER. 
= 
1-13. Ophiothrix versicolor, From N. C. Apostolideés, Anatomie et Développement des Ophiures. Archives de 
Zool. Exp. et Gén., X., Pl. XI., 1881. 
1. Egg. m, outer envelope ; y, yolk ; v, germinative vesicle ; 2, nucleus. 
2, 3, 4, 5. Different stages of segmentation. 
6. Blastosphere. 
7. Blastosphere. e, ectoderm cells. 
8. Older than fig. 7. ¢, ectoderm; y, yolk cells. 
9. Older stage ; lettering as before. First appearance of the limestone rods of the Pluteus. 
= 
Oo 
- Still older stage ; 7, the limestone rods of the Pluteus have increased in size. 
. Slightly older ; the digestive cavity, d, is outlined. 
. The embryo assumes somewhat the Pluteus outline. 
. Young Pluteus seen from the dorsal side. p, general cavity ; /, limestone rods ; a, anal region of the digest- 
ive cavity. 
a 
wore 
14-26. Ophiothrix fragilis. From J. Miiller, Ueber die Ophiurenlarven des Adriatischen Meeres, Berlin (Pt. 5), 
(1851,) Pls. VI., VIL, VIII. Abhand. d. K. Akad. d. Wiss., Berlin, 1852. 
14-17. Younger stages of the Pluteus. m, mouth; d, digestive cavity. 
18. Plutens at a stage in which all the arms are developed, although the two long arms have by no means reached 
their full length (see fig. 19). m, mouth; 0, esophagus; d, digestive cavity ; 7, intestine; w, w!, lateral 
disks of water-tubes ; ¢, lobed water-system. 
19. Plutens of same, in which the two long arms have reached their full length ; lettering as in fig. 18. 
20. The long arms of the Pluteus alone remain (extremities omitted) ; the others have been mostly resorbed ; the 
young ophiuran has assumed a pentagonal outline ; the plates of the abactinal system, the terminal arm 
plates, and the interbrachial plates, are represented by y-shaped rods. ¢/, terminal lobes (tentacles) ; 
#, actinal lobes ; ¢, second pair of lobes. 
21. Pentagonal Ophiothrix, seen from the dorsal side : the teeth are seen through the disk. 
22. The same as fig. 21, seen from the actinal side, the arms folded towards the actinal opening, showing also the 
hooks, the teeth, and the true mouth in the depth of the central star-shaped mouth. 
23. Slightly older, seen in profile : the long arms of figs. 20-23 are still of full length. 
24. A young Ophiothrix after the loss of the two long arms, seen from the dorsal side. 
25. Somewhat older than stage of fig. 23, seen from the actinal side. 7’, 1, ¢?, ¢8, terminal, actinal, and second 
and third pairs of tentacles. 
26. Young Ophiothrix, seen from the abactinal side, with two arm-joints. All traces of the Pluteus have dis- 
appeared. 
27-34. Phuteus bimaculatus. From J. Miiller, Ueber die Ophinrenlarven des Adriatischen Meeres, Pls. IV., V., 
quoted above. 
27. Shows the young ophiuran at the time when the arms of the Pluteus begin to be resorbed and the tentacular 
lobes are arranged in a horseshoe shape round the actinostome ; lettering as in fig. 25. 
28. Somewhat older stage, seen from the actinal side ; the young ophiuran has assumed a pentagonal outline; the 
terminal arm plates and the interbrachial plates are well developed; the actinal tentacles are bent in 
towards the centre of the actinostome. 
29. Still older stage, also seen from the actinal side, with three pairs of tentacles. 
30. Somewhat older stage, seen from the abactinal side; the plates of the disk, the centrodorsal, radials, and 
intermediates, are well developed. 
