PLATE 7 



EXPLANATION OF FIGURES 



34 Oblique sagittal section of an embryo somewhat more advanced than 

 that in figure 33. Digestion of the yolk has begun; clear masses of transformed 

 yolk occupy the center of each entoderm cell, while in the ectoderm the yolk 

 has formed several irregular masses in each cell. The anterior ectoderm has 

 become vacuolated. Between ectoderm and entoderm muscle cells are form- 

 ing from mesodermic elements. Brain has differentiated and the internal epithe- 

 lial rod has grown inward through the indistinct mass of pharyngeal muscle 

 cells. Position of the mouth indicated at m. X 530. 



35 Oblique sagittal section showing brain, eye pigment cell, entoderm and 

 muscles. X 530. 



36 Transverse section of same embryo as that shown in figure 27, but farther 

 posteriorly, passing through the cells which later form the esophagus. X 530. 



37 Oblique sagittal section of an older stage than that shown in figure 34. 

 Entodermic yolk completely transformed (does not stain with iron haemotoxylin) 

 while that in the ectoderm exists as large spheres. Pharynx distinct and early 

 vitellogenous cells {vit c.) differentiated. Cilia have developed. X 730. 



38 Transverse section of pharynx to show its musculature, and internal and 

 external epithelia. X 730. 



39 Tangential section through body wall of an embryo which had become 

 freed into the mesenchyme of the mother. Muscle cell (m. emh.) from which 

 extend fine muscle fibrils; the latter become the definitive sub-dermal fibers. 

 X 1016. 



40 Portion of a transverse section of the dorsal body wall showing outer 

 circular and inner longitudinal sub-dermal muscle fibers. X 1016. 



41 Adult sub-dermal muscle fibers. X 1016. 



ect., ectoderm pct.s., punktsubstance 



ent.2, secondary entoderm ph., pharynx musculature 



e.-p.c, eye pigment cell ph.ep.int., internal pharyngeal epithe- 



esoph., esophagus lium 



g.c, ganglion cells ph.ep.ext., external pharyngeal epithe- 



gon., gonad lium 



m., mouth t.y., transformed yolk 



m.emb., embryonic muscle cell vit.c, vitellogenous cells 



m.f.c, circular muscle fibers y., yolk 



m.f.l., longitudinal muscle fibers 



552 



