32 



EilBEYOLOGICAL MONOGEAI'HS. 



PLATE IX. 



Development of the C'TENornoRA. Figures from AleXj\jider Agassiz, and Cakl Chun. 



B. Up. 



E. eh. 



. e h. t. 



G. ga. 



ga.^ 

 H. hb. 

 h. lib. 

 0. oaj. 



ol. 



Blastopore. or, 



Epiblast(?) A superficial layer of V. piij. 



" small cells." p I'l. 



Tentacular bulb, an eminence formed S. sph. 



in part of epiblast, which later de- T. ta. 



velops into a tentacle. V. vl. 



Stomach. vt. cl. 



Storaoiheum. f. 



Hypoblast. ij. 



Lateral tube. B. 



Otocyst.  «. 

 Otolith. 



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. 



Figures 1-33 on this plate were arranged by A. Agassiz. 



1-37. From Agassiz, Embryology of the Ctenophoi-ae, Mem. Acad. Arts and Scicncrs, Vol. X. No. III. PL I. figs. 

 1, 2, 4, 5, 8, 12, 17, 18, 28, 29, 31, 37, 38. PI. IV. figs. 8, 19, 23, 25, 28, 32, 34, 38, 42, 45. PI. V. 

 Hgs. 1, 2, 3, 5, 6, 7, 12, 15, 18, 19, 26, 27, 29, 30. 



1-8. Beroe(Idijia) roseola. 



1. Ovumof^eroe just after fecundation. The ovum is surrounded by a transparent envelope (s"). ppl. Layer of 



granular protoplasm, vl. Vitellus. 



2. First change in the ovum by which the "genninal layer" is concentrated at and about one pole, "the 



formative pole" (B). The envelope f is gone. vt. Vitellus. 



3. Somewhat older ovum with a prominent projection of the protoplasm at the pole (8). vt. Vitellus. If the 



eminence (B) be seen from a plane at right angles to figure 3, two prominences apix-ar. 



4. An embryo in which the projeetion has increased in size, and been deeply divided by a transverse furrow. 



Each elevation is lettered eb.^ vt. Vitellus. 



5. 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'). 

 e b. Epiblast (?) 



6. The "bent dumb-bell stage," in which there are four yolk masses, the additional pair formed from the last 



by a fresli plane of segmentation. The pairs last foi'med are unitiul by a bridge, as sliown in the figure. 



7. Embryo witli four large vitelline masses, which will hereafter be lettered vt. cl., and as many epiblastic prom- 



inences (e b). 



8. 9. Dumb-bell .stages of Pleurobrachia rhododadijla, seen from oral side, divided into eight vitelline masses. 



eb. Epiblast. vl. cl. Vitelline cells. 



10. Beroe roseola, "Side view of (the) yolk-mass, in which the actinal segmcufcition of the smaller cells has com- 



menced to form sixteen unequal masses." Agassiz. 



11. An embryo witli smaller spheres {e h) more numerous, vt. cl. A'itellinc spheres. 



12. "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 rajiid segmentation, to be accomplislu'd as in earlier stages of segmentation." Agassiz. 

 c b. Epiblast. gn.^ Gastrula cavity, vt. cl. Vitelline cells. 



13. Embryo in which the sniiiller cells of the outer layer have undergone further division. 



