566 



KNOWER. 



Fig. ^-i,. Median sagittal section of disc, Figs. 19 or 19a; sc, serosal cells; 

 am.f., amniotic fold ; ul.p. (mes.), under-layer or mesodermal plug ; a.ec, anterior 

 ectoderm ; }'c., yolk-cell. Seven nuclei in various stages of division. (0.004 mm. 

 thick.) 



Fig. 34. Median sagittal section of an embryo slightly younger than that in 

 Fig. 22: sc, serosal cells; _y., yolk-mass of finely fragmented bodies beneath 

 embryo ; am.f., amniotic fold ; o.amc, opening into amniotic cavity ; a.ec, anterior 

 ectoderm ; ul.p. (fnes.), anterior end of mesodermal plug ; ^fc, yolk-cell ; p.yi., per- 

 forated yolk body. Six dividing nuclei are seen. (0.004 mm. thick.) 



Fig. 35. Median sagittal section of embryo at stage Fig. 24 : c^., chorion ; 

 am., amnion; am.c, amniotic cavity, now completely closed; sc, serosal cells; 

 a.ec, anterior ectoderm ; yc, yolk-cells ; til.p., mesodermal plug ; mes., mesoderm. 

 Seven dividing nuclei in different phases. (0.004 inni- thick.) 



Fig. 36. Median sagittal section of embryo, between Figs. 24 and 26, with 

 anterior end square: sc, serosal cells; s., serosa; am., amnion; am.c, amniotic 

 cavity ; a.ec, anterior ectoderm ; 7nes., mesoderm ; yc, yolk-cell ; yb., yolk body. 

 Ten dividing nuclei in different stages. (0.004 mm. thick.) 



Fig. 37. Median sagittal section of embryo in Fig. 27 (or 26) : am.p., amnion 

 at posterior end; am.a., amnion, thinned out at anterior end; amc, amniotic 

 cavity ; mes. p., mesoderm under posterior end ; mes., mesoderm in the middle 

 region ; mes.a., anterior limit of mesoderm ; ect.cp. (anterior ectoderm as in previ- 

 ous figures a.ec), now ectoderm of cephalic region ; p.yb., perforated yolk body ; 

 yc, yolk-cells, nuclei in large masses of protoplasm. Nine dividing nuclei. (0.004 

 mm. thick.) 



