MARGINAL CELLS 

 CENTRAL CELLS \ 



EIGHT-CELL STAGE 

 IRD 

 EM 

 ARCINAL CELLS 



' -^ / "" 



FOURTH CLEAVAGE 

 EGG 

 CENTRAL C"ELLS 



rHT rFLL STAGE FOLLOWING THIRD CLEAVAGE, 

 EGG INTACT BLASTODERM HEMOVED FROM 



/ CEI 



, ?• * "^ yrvw 



7^« 



FIFTH CLEAVAGE 



^a,?*""'''*^'^^ 



MESODERM 



>*^ 



LATE BLASTODERM NOTOCHORDAL CANAL '^"TERIOR NEUROPORE 



(SAME AS E) (EXTE8NAL OPENING) \ NEURAL FOLDS 



EAD FOLD 



NOTOCHORDAL CANAL EPIMERIC MESODERM EPIDERMAL TUBE^ 



EPIDERMAL TUBE HEAD OUTGROWTH . NEURAL TUBE 



(ECTODERM) ' -^. . . 



Fig. 231. Series of diagrams, showing stages in the development of the turtle. (A-F) 

 Cleavage stages after Agassiz. (G-J) Stages of gastrulation, drawn from slide prepara- 

 tions. (K-T) Stages during development of body form. f-P, Q, T from Agassiz; the 

 others are original.) (See L. Agassiz, 1857, Cont. Nat. Hist, of U. S. A., Vol. II.) 



479 



