PLATE 3 



EXPLANATION OF FIGURES 



4 A transverse section through the sensory vesicle, hypophysial duct, 

 definitive ganglion, and subneural gland of an embryo. It is reproduced to 

 show especially the developing lenses within vacuoles of lens cells, the similarity 

 of lens cells and nerve cells of the retina, and the relation of the pigment granules 

 of the pigment cup to the bodies of the retinal cells. 



5 A drawing of the sensory vesicle and its sense organs as viewed from the 

 dorsal side of a living tadpole. 



6 A slightly oblique transverse section through the nervous system in the 

 plane of the statolith cell, the latter displaced slightly by the knife. The entire 

 series of lenses and their position in the axis of the pigment cup are shown. 



7 A sagittal section of the middle adhesive papilla, showing its tubular 

 structure and its content of mesenchyme cells. 



8 A transverse section of the tail, showing the horizontal fins; the struc- 

 ture of the notocord; the muscle cells, four on the dorsal and four on the ventral 

 side of the notocord; the cut ends of muscle fibrillae in the cortical layer of the 

 muscle cells; the hollow nerve cord on the left side of the notocord in the space 

 between the edges of the muscle bands; the endodermal strand in the correspond- 

 ing position on the right, and the mantle sheath closely applied to the muscle 

 band beneath the tunic. 



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