FORMATION OP GERMINAL LAYERS IN CHELONIA. 47 



15. C. F. Sarasin. — " Reifung u. Furchung der Reptilieneier," ' Arb. aus d. 



Zool.-Zoot. Inst. Wiirzburg,' Bd. vi, 1883. 



16. C. K. Hoffmann. — " Beitrage zur Entwicklungsgeschichte der Repti- 



Hen," ' Zeit. f. Wiss. Zool./ 1884. 



EXPLANATION OF PLATES II, III, IV, and V, 



Illustrating Mr. K. Mitsukuri's Paper on " The Formation of 

 the Germinal Layers in Chelonia." 



List of Reference Letters. 



«. 0. Area opaca. «. ^. Area pellucida. «ot. Amnion, ar. Line along which 

 nuclei are specially heaped up in the germinal wall. Figs. 18 and 20. — bl. 

 Blastopore. bl. p. Blastoporic passage. ck, Notochord, ect. Ectoblast. 

 en, Entoblast. enc. Chorda entoblast. end. Darm entoblast. y. to. Ger- 

 minal wall. h.f. Head-fold. mes. Mesoblast. n. Nuclei in the yolk. 

 si. " Sickle." V. o. Ventral opening of the blastoporic passage, yk. Yolk. 

 yk. c. Yolk-corpuscles, yk. p. Yolk-plug. z. Shelf-like extension into the 

 archenteron. 



All the figures, excepting Figs. 5, 6, 14 «, 16, and 35, have been drawn by 

 C. Ishikawa. Figs. 1 — 6 and 35 have been re-drawn by M. Indo. 



Figs. 1 — 4 have been drawn with Zeiss's A A, x 2 ; Figs. 7 — 17 with 

 Zeiss's C C, X 2 ; Figs. ] 8—34 with Zeiss's D D, x 2 ; Fig. 35 with 

 Zeiss's B B, X 2 ; Fig. 5 not drawn to scale ; Fig. 6 is a diagram. 



Fig. \a. — Dorsal view of the embryonic shield from an egg just deposited. 



Fig. 1^. — Ventral view of the same. 



Fig. 2 a. — Dorsal view of the embryonic shield from an egg laid forty-eight 

 hours. 



Fig. 2 b. — Ventral view of another embryonic shield of the same age from 

 the same deposit. 



Fig. 3. — Dorsal view of the embryonic shield from an egg laid thirty-six 

 hours. 



Fig. 4 a. — Dorsal view of an embryo from an egg laid three days. 



Fig. 4i. — Ventral view of the same. 



Fig. 5. — Ventral view of an embryo from an egg laid five days. 



Fig. 6. — Diagram of the embryonic shield. 



Figs. 7 — 15. — Series of transverse sections of the embryonic shield given 

 in Figs, la and b, arranged from behind forward. 



