INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 251 



live in dark caves and depths of the sea, or in the earth itself, shouhl 

 lose their power of vision, their eyes being reduced to almost nothing. 



But we know that in the depths of the sea where some eyeless 

 animals occur, whoso deprivation of eyes is explained by the darkness 

 prevailing, there also exist forms which have not merely ordinary 

 eyes, but unusually developed, large, prominent, and deeply pigmented 

 eyes. The Gnathophausia of the ' Challenger ' expedition, from 1830 to 

 4020 metres, actually possesses pedunculate eyes, and, besides these, 

 ocelli on the maxillae; the Memida, from 1000 to 1200 metres, has well- 

 developed and exceedingly sensitive eyes ; while Gammaracantlms 

 caspius fx'om 108 fathoms, Boeckia spinosa, nasuta and hystrix from 70 

 to 150 fathoms in the Caspian, and various species of 3[ysis from the 

 same sea and from depths down to 500 fathoms, all have well-developed, 

 large, prominent, and black pigmented eyes. This sufficiently proves 

 that at these depths the visual organ is made use of, as here absolute 

 darkness does not prevail, but more properly only a dark night. We 

 have only to remember that nocturnal animals such as owls, predaceous 

 mammals, &c., possess very large and well-developed visual organs 

 (in fact, eyes adajited to the darkness), to explain the established fact 

 that the depths of the sea are inhabited by Crustaceans in which the 

 visual faculty is enormously increased. But seeing that, as has been 

 said, forms of animals also exist in the same abysses whose eyes are 

 but slightly developed or unpigmented, or even appear completely 

 reduced to a rudimentary condition, it is evident that the explanation 

 that tlie retrogression of the eyes is produced by living in the depths 

 of the sea is not sufficient. 



In the Caspian Sea, Dr. Grimm obtained fifteen new species of 

 Gammaridfe (^Gammarus pauxillus, G. crassns, G. Gregrokowii, G. por- 

 teniosus, G. coronifer, G. thaumops, Pandora cceca, Ipliigeneia abys- 

 soruni, Gammaracanthus caspius, and Amathilinella cristata), all of 

 which are furnished with eyes, but in very difltcreut degrees of de- 

 velopment : thus G. caspius has very large round eyes, G. coronifer 

 and Amathilinella cristata long but narrow eyes, G. thaumops triangular 

 unpigmented eyes, and Pandora ceeca small unpigmented eyes, which 

 can hardly be endowed with the faculty of sight. 



Five other species (Oncsimtis caspius, 0. pomjjosus, 0. platyuros, 

 Pantoporeia microphthalma, and Nipharcjus caspius) furnish even a still 

 better illustration that eyed and eyeless may live together. Thus 

 Pantoporeia macrophthalma and Niiihargus caspius have pigmented 

 but small eyes. Of the species of Onesimus, some have red, others 

 (0. caspius) perfectly unpigmented eyes, whicli in tlie latter si>ecies 

 at least arc altogether deprived of the power of sight ; with these 

 more or less blind forms, there live a number of Mysidic, the large, well- 

 developed eyes of which certainly absorb sufficient light even in the 

 darkness of the depths. 



It having been sIkjwu that doep-.sea existence alone does not of 

 necessity cause the retrogression of the visual organs, the author pro- 

 ceeds to show by what the disa])pcarance of the eyes is essentially 

 brought about and by what tliey are replaced. Whilst admittedly the 

 quantity of light is very small, at a c-eitain distance from the surface 



