606 AMPHIBIANS 



only 0.3mm. in Hypogeophis. The rotatory muscles are present in both 

 genera (lacking in Ccecilia and Herpele), though thin and largely ten- 

 dinous, and incapable of moving the eye owing to its attachment to the 

 overlying skin. In the larva, a retractor bulbi is properly attached to the 

 globe, but in later development it is seduced away by the tentacle to 

 become its retractor. The internal rectus serves to retract the tentacle 

 sheath, and a former levator bulbi is pressed into service as a compressor 

 muscle of the tentacular (Harderian) gland. 



The eyeball lies beneath a transparent patch of skin, from which it 

 is separate only in the larva. In Hypogeophis, the primary cornea, a 

 continuation of the fibrous sclera, can still be identified after fusion with 

 the skin in the adult; but in the adult Ichthyophis the sclera appears to 

 intersect the corium of the skin, and the lens to contact the latter directly. 

 The chorioid is very thin, and is pigmented in Ichthyophis but not in 

 Hypogeophis. There is no ciliary body or any mechanism of accommo- 

 dation, and the iris consists entirely of the two epithelial retinal layers, 

 only the anterior of which is pigmented. The pupil is the same size as 

 the lens, which projects half-way through the aperture. The relatively 

 large lens is solid, somewhat flattened, and is cloudy in life (in Hypo- 

 geophis, at least) . Running through the small vitreous cavity from retina 

 to lens, in the position of a canal of Cloquet, is a strand of (meso- 

 dermal?) tissue. 



The retina is quite respectable. There are no vitreal vessels. The pig- 

 ment epithelium bears many fine, pigmented processes, in which there 

 is no pigment migration. Only massive rods, simple in structure (no 

 oil-droplets or paraboloids) are present. In Hypogeophis the outer nu- 

 clear layer has two to three rows of nuclei, the inner nuclear three, and 

 the ganglion layer two. Corresponding figures for Ichthyophis are: 2, 

 2-3, 1. In the latter genus the optic papilla is triple, the three branches 

 of the optic nerve lying in one vertical plane icf. Polypterus) . No optic 

 chiasma is visible outside the brain. 



