5o6 SCIENCE PROGRESS. 



likewise the vitreous humour. Optic nerve and eye muscle 

 are present but very slender and long-. 



In 1 89 1 the eggs of this Goby were found attached to 

 the lower side of the rocks beneath which the fish lives, and 

 in the embryo before hatching the development of the eyes 

 was found to be perfectly normal, and similar to that which 

 takes place in other fish embryos. 



In the eye of Proteus a progressive development of the 

 lens in the embryo and its subsequent degeneration and 

 total disappearance in the adult have been definitely observed 

 by Schlampp (1892). It develops normally from the epi- 

 blast and sinks into the opening of the secondary optic 

 vesicle where it is still to be found in the hatched larva. It 

 does not advance however beyond the embryonic cellular 

 structure, and in quite young animals is already much re- 

 duced in size ; in the adult not a trace of it remains. The 

 vitreous body is also absent in Proteus, the retina and optic 

 nerve are present. The retina in consequence of the 

 absence of the vitreous body does not spread out flat but 

 forms a solid spherical mass whose histological structure is 

 not markedly different from that of other Amphibia, but the 

 terminal elements (rods and cones) do not reach their perfect 

 form. In the Mole (Talpa) the lens is present though it 

 retains its embryonic cellular structure throughout life, and 

 in this respect is more rudimentary than the lens of Typhlo- 

 gobius. The choroid is but slightly developed, and has 

 little pigment, while the pigment layer of the retina is 

 highly developed. The cellular layer of the retina is 

 present but not fully differentiated ; rods and cones according 

 to Kohl are both present. The vitreous body is also 

 present, and likewise the optic nerve, which Semper stated 

 to degenerate in adult life. 



Three species of blind crayfishes are known which 

 inhabit subterranean waters in North America, in Missouri, 

 Kentucky, and Tennessee. They are Ca^nbarus pellucidus, 

 Tellkampf ; C. hamtLlatus, Cope and Packard ; and C. setosiis, 

 Faxon. The eyes in these, to superficial observation, 

 appear to be absent. The eye-stalks are present but they 

 terminate in a blunt cone instead of a bulbous enlargement, 



