REPRODUCTION AND DEVELOPMENT 



49 



eight-coll stage is formed. This stage has four smaller, deeply pig- 

 mented cells and four larger, lighter-colored cells; cleavage in the 



.po/ar docfy 



perMteJ///1^ 

 apace 



pronuc/ef 



rcrtilizatbn 

 memtiraoe 



.po/ar body. 



blastula 

 cot^Jty 



ectocferm archenteron endoderm 



t>/astu/a 

 cav/ty^ 



ventro/ lip 



f per/77 r/n^' 



^erm ring.. 



ilastoDore reurai p/ate notocfTordai p/ate 

 ecCoderfv \ /o/a^topora 



Anterior end , 



endoden 



arc/tenteron 



Ventrai surface 



H 



Fig. 31. — Early development in the amphioxus. A, one-cell stage, in section; 

 the arrow indicates the egg-axis. B, eight-cell stage, from the surface. C, 

 thirty-two-cell stage, from the surface. D, early blastula, in section. E, late 

 blastula, as if cut in half. F , early gastrula, in section. G, gastrula, from 

 the surface. R, late gastrula in section, oriented to show dorso-ventral and 



antero-posterior axes. 



(4, B, and G, from E. G. Conklin, 1933, Jout. Experimental Zoology, vol. 64; C-F and 

 n from E. G. Conklin, 1932, Jour. Morphology, vol. 54.) 



frog's egg is total but unequal. Make two drawings of this stage, one 

 from the side view and the other as seen from the animal pole, indi- 

 cating the poles and furrows as before. 



