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EXPLANATION OF PLATES. 



I. 9.5 mm. embryo, X250. Diagrammatic anterior view of eyes to show relation of 

 electric tissue (stippled) to eye-muscles. 



R. Ex Rectus externus muse-In. O. Inf Obliquus inferior muscle. 



R. Int Rectus interims muscle. O. Sup Obliquus superior muscle. 



R. Inf Rectus inferior muscle. Ex. C External carotid artery. 



R. Sup Rectus superior muscle. 



II. 20 mm. embiyo, X200. Diagrammatic anterior view of eyes to show increase of 

 electric tissue (stippled) and relation of cranial nerves to eye-muscles. 

 Roman numerals indicate cranial nerves. 



III. 20 mm. embryo, X475. Diagrammatic median view of left eye. 



IV. 33 mm. embryo, X200. Diagrammatic anterior view of eyes to show relation of 



nerve III to eye-muscles and to the four separate electric organs (stippled). 



To left is shown the electric branch of nerve III and to right the oculomotor 



branch. 

 V. Rectus interims muscle. Four stages to show gradual growth and differentiation of 



electric tissue on the young muscle. 

 Fig. 1. 4 mm. embryo. Cross-section. Electric area slightly darker than muscle 



area. 

 Fig. 2. 9.5 mm. embryo. Cross-section. Electric area increased in size and 



staining capacity. 



Fig. 3. 14 mm. embryo. Oblique section. Electroblasts multinucleate. 

 Fig. 4. 20 mm. embryo. Cross-section showing only a portion of the electric 



area. Electroblasts vacuolated. Myoblasts striated. 



El Electroblast, multinucleate. Un. N Undifferentiated nucleus 



M Myoblast. of electroblast 



V Vacuole. N Nucleus of myoblast. 



S Striations. 



VI. Electroplaxes. Three stages to show growth and differentiation of adult electroplax 



from single electroblast. 



Fig. 1. 20 mm. embryo. Single electroblast. Longitudinal section to show 

 formation of ventral papilUe from vacuoles. Nuclei Undifferentiated. 



El Electric area of electroblast. Un Nu Undifferentiated nucleus. 



N Nutritive area. S Striation. 



D. V Dorsal vacuole. P Papilla. 



V. V Ventral vacuole. 



Fig. 2. 33 mm. embryo. Longitudinal section of electroplax. Nutritive and 

 electric areas differentiated. Striations straight and regular. 



El. Nu Electric nucleus. N. Nu. . . .Nutritive nucleus. 



