MEM. M. C. Z., IX. No. 2.—ECHINODERMATA, 13 
PIGAVTME yh T : 
Development of OpururowEs. Figures from Evias Merscuntkorr, Husert Lupwic, ALEXANDER 
Acassiz, T. H. Srewart, Max Scuuntrze, and Avcust Kroun. 
(1-20, 26-33, Viviparous Ophiwrans.) 
1-14. Amphiura squamata. From E. Metschnikoff, Studien iiber die Entwickelung der Echinodermen und 
Dor 
14. 
Nemertinen. Mém. de ]’Acad. Imp. des Scien. de St. Pétersbourg, VIIe Série, XIV. No. 8, Pls. III. B, 
IV., 1869. 
67. Blastoderm. 0. Mouth. 
C3 Cutis. oe. (Esophagus. 
ce. Provisional limestone rods; probably the ho- pa. Dorsal pore of the water-system (madreporite). 
mologue of the Pluteus rods. pl. Remnant of rudimentary Pluteus. 
cpl. The bilateral embryonic skeleton. t. Tentacles. 
es. Segmental cavity. v. Rudimentary water-system. 
d. Left lateral disk. va. Water-system. 
d*, Right lateral disk. vt. First trace of digestive cavity. 
ep.  Epidermis. vv. Lobed water-system. 
me. Thin outer membrane surrounding blastoderm. vp,vr. Circular canal. 
mv. Thick inner membrane of same. 
. Egg, surrounded by its two membranes (me, mv) with the blastoderm (@ 7). 
. The same in profile : the outer egg membrane is not figured. 
Somewhat more advanced stage, showing, in addition to the blastoderm, the first indication of the digestive 
cavity (v7?) and of the large cells of the cutis (c). 
. Elongated embryo still protected by the inner egg membrane (77). The deposition of the provisional lime- 
stone rods has commenced (cc). On each side of the future cesophagus are placed the rudiments of the 
water-system (v). 
. Somewhat older embryo, with longer limestone rods (¢ p 7), seen in profile. 
. Still older embryo, seen from the dorsal side, showing the greatly enlarged water-system (v a) and its two 
lateral disks (d!, d?). 
- Somewhat older embryo, also seen from the dorsal side, showing the five lobes of the water-system (v «). 
. Older stage, remarkable for the great development of the lateral disks (d!, d?), the change in the position of 
the digestive cavity and cesophagus, the great increase in the size of the lobes of the water-system (v v), 
and the formation of a dorsal pore (p a), the future madreporie body. 
. Somewhat older embryo, showing the horseshoe-shaped water-system, each primary fold of which (vv) has 
subdivided into four secondary lobes. 
. Embryo seen in profile. The cesophagus is already surrounded by the water-system ; each fold of the water- 
system has subdivided into five smaller ones. The stone canal is most distinct. 
- An embryo about in the stage of fig. 10, seen from the dorsal side: the provisional limestone skeleton is 
already disappearing. 
. The water-system of the same embryo: v v, the blind sacs (tentacles) of the water-system ; v7, the circular 
canal ; p a, the madreporite. 
. The embryo in a stage immediately after passing from the bilateral to the pentagonal form, seen from the 
actinal side ; the peculiar arrangement of the tentacles (f) and the formation of the mouth skeleton are 
specially to be noticed in this stage. 
Somewhat more advanced than the preceding stage, seen from the dorsal side, showing the six reticulated 
plates of the abactinal surface, as well as the stem (p 7), first described by Krohn and Schultze, forming a 
temporary connection with the ovary. This becomes atrophied in still older stages. 
