54 JOURNAL OF THE [October, 



The skin is formed by a single layer of cells. The skull is a 

 capsule formed by a cartilaginous substance of varying thick- 

 ness, which in course of development ossifies. Only at a few 

 places is it perforated for the passage of nerves, blood-vessels 

 and spinal marrow. The enclosed brain shows the bilateral, 

 symmetrical form, and the white and gray substance — this latter 

 with large ganglion cells, and their nuclei. 



The eyes are enclosed by a hard skin, the sclerotica, which in 

 front becomes thinner and transparent, forming the cornea. In 

 our object the skin over the cornea is not yet perforated. The 

 eye in the larval state is still internal, and consequently the 

 animal is either blind, or at least not sharp-sighted. The 

 chorioidea, a layer of pigmented cells, lines the inside of the 

 sclerotica, leaving the iris, as a perforation in the front part of the 

 eye. In this perforation, framed like a window, lies the 

 spherical lens. 



Inside of the chorioidea is the retina, the third layer of the 

 eye. Between the cornea and the lens is the aqueous humor, 

 and between the lens and the retina is the vitreous humor. 

 This latter is of a more consistent nature than the former. 

 Retina is a complex name for different layers, formed by the 

 ends of the fibres of the optic nerve. 



The optic nerve, coming from the cerebrum, penetrates the 

 three layers of the eye, the sclerotic, the chorioid and the 

 retina ; spreads on the inner surface of the latter, radially from 

 the center to the periphery on the rear of the eye-ball ; and there 

 forms layers of ganglion cells, internal fibres, internal nuclei, 

 external fibres, external nuclei and rods and cones. These 

 rods and cones lie close to the chorioidea. 



Here is shown again the advantage of the eye of an amphibian 

 in the larval stage for microscopical observation. The different 

 layers of the retina are composed of large elements, and show 

 very distinctly ; while the eye in the mature state mostly shows 

 the retina as a thin layer, the constituent parts of which can be 

 seen only by dissection by means of needles. 



In the cavity of the mouth, the roof, as well as the surface of 

 the tongue, is covered by a membrane of ciliated cells. In the 

 tongue we see the cartilaginous formation of the bone, and 

 muscle-fibres, in both longitudinal and transverse section, prov- 



