1-37. From Agassiz, Embryology of the Ctenophore, Mem. Acad. Arts and Sciences, Vol. X. No. III. Pl. I. figs. nN, 
1, 2, 4, 5, 8, 12, 17, 18, 28, 29, 31, 37, 38. Pl. IV. figs. 8, 19, 23, 25, 28, 32, 34, 38, 42, 45. Pl. V. 
figs. 1, 2, 3, 5, 6, 7, 12, 15, 18, 19, 26, 27, 29, 30. 
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6. 
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fo] 
10. 
11. 
12. 
13. 
EMBRYOLOGICAL MONOGRAPHS. 
PLATE IX. 
Development of the Crexopuora, Figures from Auexanper Acassiz, and Cant CHUN, 
B. dlp. Blastopore. : 
E. eb. Epiblast (?) A superficial layer of 
“*small cells.” 
eb.t. Tentacular bulb, an eminence formed 
in part of epiblast, which later de- 
velops into a tentacle. 
G. ga. Stomach. 
ga.1 Stomodzeum. 
H. 2b. Hypoblast. 
L. Zt. Lateral tube. 
O. ocy. Otocyst. 
ol. — Otolith. 
Figures 1-33 on this plate were arranged by A. AGAssIz. 
1-8. Beroé (Idyia) roseola. 
Ovum of Beroé just after fecundation. The oyum is surrounded by a transparent envelope ({). ppl. Layer of 
granular protoplasm. vt. Vitellus. 
First change in the ovum by which the ‘‘germinal layer” is concentrated at and about one pole, ‘‘the 
vt. Vitellus. 
. Somewhat older ovum with a prominent projection of the protoplasm at the pole (@). 
eminence (4) be seen from a plane at right angles to figure 3, two prominences appear. 
An embryo in which the projection has increased in size, and been deeply divided by a transverse furrow. 
formative pole” (@). The envelope ¢ is gone. 
Each elevation is lettered ¢ 5.1 vt. Vitellus. 
The furrow has deepened in this stage, so that the yolk is divided into two masses. The protoplasmic super- 
ficial layer extends over and surrounds them both. The deep slit is the position of a gastric cavity (ga’). 
eb. Epiblast (?) 
The ‘‘ bent dumb-bell stage,” in which there are four yolk masses, the additional pair formed from the last 
The pairs last formed are united by a bridge, as shown in the figure. 
Embryo with four large vitelline masses, which will hereafter be lettered vé. cZ., and as many epiblastic prom- 
by a fresh plane of segmentation. 
inences (eb). 
9. Dumb-bell stages of Pleurobrachia rhododactyla, seen from oral side, divided into eight vitelline masses. 
eb. Epiblast. vt. cl. Vitelline cells. 
Beroé roseola, ‘‘ Side view of (the) yolk-mass, in which the actinal segmentation of the smaller cells has com- 
menced to form sixteen unequal masses.’’ Agassiz. 
An embryo with smaller spheres (¢ /) more numerous. 
“Yolk-mass seen from the actinal pole; the masses are arranged round a vertical axis, each small mass 
forming a small overhanging projection, at the extremity of which the germinal layer is concentrating, 
preparatory to a rapid segmentation, to be accomplished as in earlier stages of segmentation.” 
vt. cl. Vitelline cells. 
{mbryo in which the smaller cells of the outer layer haye undergone further division. 
eb. Epiblast. ga.’ Gastrula eavity. 
vt. cl. Vitelline spheres. 
Mouth. 
Pigment. 
Layer of protoplasm (?) 
Funnel. 
Tentacle. 
Vitellus. 
Vitelline cells, ‘‘ cell masses.” 
External envelope. 
Swimming flappers. 
Polar elevation of protoplasm (?) 
Prominences of the body walls on 
each side of the otocyst. 
vt. Vitellus. If the 
