FIG. 269 



270 



272 



Figs. 269-283. — Development of Teleost, Serranus atrarius. (After H. V. WILSON.) 

 Fig. 276 X 25. 269. Egg immediately prior to segmentation, showing position of germ 

 disc and of oil globule, 270. Germ disc after first cleavage. 271. Germ disc after third 

 cleavage. 272. Vertical section of blastula. 273. Vertical section of blastula, showing 

 origin of periblast. 274. View of marginal cells of blastula of similar stage. 275. Growth 

 of blastoderm around yolk mass, 276. A slightly later stage, showing growth of embryo. 

 277. Continued growth of embryo and reduction in size of the blastopore. 278. Sagittal 

 section of tail region of embryo of last figure. 279, 280, 281. Cross-sections of embryos, 

 showing successive stages in the development of notochord, gut, neuron, mesoblast. 282. 

 Cross-section of young embryo, showing the mode of formation of gill slit. 283. Embryo 

 shortly before hatching. 



A. Anus. A U. Auditory vesicle. BP. Dorsal lip of blastopore. CH. Notochord. 

 EC. Ectoderm. EN. Entoderm. G. Gut. GD. Germ disc. GR. Germ ring. GS. 

 Gill sUt. H. Heart. HP. Head process. AT'. Kupffer's vesicle. M. Spinal nervous 

 system. MES. Mesoblast. MP. Marginal periblast cells. OG. Oil globule. OL. Ol- 

 factory pit. OP. Optic capsule. P. Periblast. PS. Primitive segments. SC. Segmen- 

 tation' cavity. SCH. Subnotochordal rod. TM. Tail mass. Y. Yolk. 



20S 



