PLATE 6 



EXPLANATION OF FIGURES 



25 Drawing from life of an embryo at the stage seen in the preceding sec- 

 tion (fig. 24). The globular nature of the free yolk is well shown. Water had 

 infiltrated under observation between capsular meml)rane and yolk. Stained 

 intra vitam with neutral red. X 730. 



26 Frontal section of an embryo at same stage as that in preceding figure. 

 Same features as in the latter and also the secondary entoderm cells {ent. 2). 

 X 520. 



27 Transverse section through pharynx and most anterior entoderm cells. 

 Internal pharyngeal epithelium clearly illustrated in section, and the cells which 

 are to form the pharynx musculature are grouped around this epithelial rod. 

 X520. 



28 Frontal section of anterior end of an embryo to illustrate position of the 

 two eye pigment cells. X 1016. 



29 Oblique transverse section through brain and posterior nerve trunks. 

 X 730. 



30 Series of drawings to show one type according to which the pigment 

 granules of the eye appear one after another. X 530. 



31 A second series to show another type of melanin deposition whereby 

 several tiny spherules appear together and enlarge gradually. X 530. 



32 Eye of an older embryo which had escaped from its capsule. Pigment cell 

 has become invaginated by pressure of the ganglion cell {(j.c.) from which nerve 

 fibers extend into the brain. X 730. 



33 Adult right eye seen from above showing the sight cell at the end of the 

 optic nerve. X 730. 



6r., brain 



ect., ectoderm 



ent.l, primary entoderm 



ent.2, secondary entoderm 



e.p.c, eye pigment cell 



esoph., esophagus 



g.c, ganglion cells 



inf., infiltration 



m.emb., embryonic muscle cell 



mes., mesenchyme 



mes-ect., mes-ectoderm 



n., nucleus 

 n.op., optic nerve 

 n.p., posterior nerve trunk 

 pct.s., punktsubstance 

 ph., pharynx musculature 

 ph.ep.int., internal pharyngeal epithe- 

 lium 

 t.y., transformed yolk 

 vest.ep., epithelium of vestibule 

 y., yolk 



550 



