EYE OF NOTORYCTES TYPHLOPS. 565 



as also the gland and duct, wliicli leads either into a con- 

 junctival sac, or direct into the nasal cavity. The optic 

 nerve, on the other hand, is about in the same stage of 

 degeneration as in Notoryctes, there being no connection 

 with the brain. 



In Typhlops all parts are comparatively well developed, 

 the large glands, with their blind ducts towards the skin, 

 being, however, very like those of Notorj'ctes, though the 

 destinations of the internal ducts are different. 



In Rhineura the most degenerate of previously-described 

 eyes in burrowing animals the muscles and conjunctival sac 

 are absent, though the gland is well developed. The lens is 

 found but rarely, and a single cartilaginous bar is present in 

 the sclero-choroid. 



In the presence of a choroid split, and the general struc- 

 ture of the retina, this eye resembles the higher stage of 

 that of Notoryctes, and, in the absence of an iris epithelium, 

 the lowest stage. 



Scalops and Talpa are so much less degenerate than 

 Notorj'ctes that a compai'ison is needless. 



It is, therefore, not possible to compare the eye of 

 Notoryctes with that of any other animal in to to, but, 

 omitting the lachrymal glands and ducts, which are well 

 developed in all burrowing animals, and the muscles con- 

 nected Avith the hbrous capsule, its higher stages are almost 

 identical with that found in Troglichthys, which is regarded 

 by Eigenmaun as the most degenerate of vertebrate eyes. 

 Thus it will be seen that the more degenerate condition 

 found at present in Notoryctes is without a parallel among 

 the Vertebrata, consisting simply of a fibrous sclero-choroid 

 containing a hollow pigment ball filled with a mass of cells, 

 devoid of all arrangement, and without any nerve or blood 

 supply. 



The presence of such abnormally well-developed lachrymal 

 glands and of the ducts in all burrowing animals — except 

 Scalops and Talpa, where they are as yet unaffected — is most 

 interesting. The blind outer duct present in Typhlops, and 



VOL. 50, PART 4. NEW SERIES. 41 



