PLATE I 



EXPLANATION OF FIGURES 



All figures were outlined with a Zeiss camera-lueida, at the level of the stage 

 of the microscope. Lens used: Zeiss apochromatic immersion 2 mm., 1, 40. 

 Artificial light (gas). 



1 Transverse section of an embryo of Fundulus, three days old. Fixation: 

 Regaud; stain: fuchsin-methylgreen. Ocular 4. P, pigment cells. 



2a Surface view of an epidermic cell (upper layer) of an embryo of Fundulus, 

 nine days old. P'ixation: Benda (without acetic acid); stain: fuchsin-methyl- 

 green. Ocular 8. 



2b Epiderm of an embryo of Fundulus, nine days old: perpendicular sec- 

 tion. Two layers of cells and glandular cell. Fixation: Regaud; stain: fuchsin- 

 methylgreen. Ocular 12. 



3 Section perpendicular to the epithelium of the branchial region in an em- 

 bryo of Fundulus, nine days old. Pharyngeal epithelium and peculiar mesen- 

 chyme-cells. Fixation: Regaud; stain: fuchsin-methylgreen. Ocular 12. 



