EXPLANATION OF PLATES. 



PLATE 1. 



1. Plaster reconstruction of the brain and Cyclopean eye of embryo Xo. 5.59. X 25. Cranial nerves art; marked with 



Roman numerals, n. v., optic vesicle; s, snout; m, mouth. 

 '2. View of the right side of embryo Xo. 559. X 9. Only the face region is worked out in detail. {'. <., umbilical 



vesicle. 



3. Face of embryo Xo. 559. X 16. The drawing is made from a plaster-of-paris reconstruction. S, snout. 



4. View of the left side of Cyclopean embryo Xo. 559. X 9. The'drawing was made directly from the .specimen in 



formalin. 



PLATE 2. 



1. From the photograph of embryo No. 201. X 1|. 



2. Photograph of ovum, No. 559. X 1. 



3. Section through the cyclopean eye, No. 1165. X 40. E, eye; f. L, eyelid. Behind the eye are seen the ocular 



muscles. 



4. Section through the external ear of embryo Xo. 201. X7.5. There is an invagination of the epidermis and 



tissues of the ear are dissociated. 



5. Photograph of the ovum, Xo. 559, showing the embryo in position. X 3. The exoccelom is filled with a dense 



magma. 



6. Outline of brain of embryo X T o 1201. X 100. From a plaster reconstruction made by Dr. Bartelmez. The wide- 



open flange in front contains two depressions, the optic vesicle, which unite through a common groove, the torus 

 optieus, as marked on the drawing. The depression behind this flange no doubt represents the cavity of the 

 midbrain and hindbrain. This specimen is No. 87 of the collection of the University of Chicago and con- 

 tains eight pairs of myotomes. 



7. Phot ograph of section through the snout of specimen Xo. 559. X 60. The frontal process contains the common 



cerebral vesicle, c. v., and below the snout there is the upper jaw, . j. 



PLATE 3. 



All the photographs are from the sections of the embryo Xo. 559. Figs. 1 and 2, X50; figs. 3, 4, 5, X40. 



1. Section through the ocular muscle, showing the terminal fibrils of the third and sixth nerves. Oc. mus., ocular 



muscle; n, notochord; m, mouth; v, fifth nerve. 



2. Section through the eye at its attachment to the interbrain. T. o., torus opticus; v', v", v'", branches of the 



fifth nerve; iy*, terminal filaments of the fourth nerve ending in the primordia of the superior oblique muscle 



3. Section through the lower tip of the cerebral hemisphere The peculiar tissue surrounding the nerve-body may 



represent a degenerated olfactory region. About this is seen a section of the interbrain, and below a process 

 containing the cyclopean eye. Fb, first branch of fifth nerve; m, mouth. 



4. Section through the middle of the cyclopean eye. I. b., interbrain; Fb, first branch of fifth nerve; m., mouth. 



5. Section through the cerebral hemispheres as they communicate with the interbrain. I. b., interbrain; c. h., cerebral 



hemisphere; s, snout; u. j., upper jaw. Over the lamina terminalis is seen the peculiar thickening of the out- 

 side of the body which may represent the degenerated olfactory region also shown in the flat section of figure 3. 



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