Y. 
DAEKNESS AND EYES 
[Abstract]. 
Ey Sidney E. Harmer, B. A., B.Sc. 
Read 2gtli January, 1884. 
The visual organs of animals wliicli have lived during many 
successive generations in total, or nearly total, darkness, exhibit 
much departure from the normal type. Such animals may he 
grouped as follows ; — (1) Those that inhabit caves. (2) Deep-sea 
forms. (3) Pelagic animals. (4) Parasites which live within the 
bodies of their hosts. 
The Cave animals have been especially studied in the United 
States and in Austria ; as, for example, in the Mammoth Cavern in 
Kentucky, which consists of many miles of perfectly dark galleries, 
excavated by the action of water on the limestone rock ; and in 
many others in different parts of North America. The Austrian 
caverns are smaller, and are situated to the north of the 
Adriatic Sea, near Trieste. 
Schiodte has divided the Cave fauna into four groups. The 
Shade animals, which are found near the mouths of the caverns, 
and which differ little from those living outside ; Twilight animals, 
inhabiting darker recesses ; — these have small eyes, the comparative 
absence of light having rendered their visual organs of little use ; — 
the. Cave animals proper, of which a large proportion are perfectly 
blind ; and, lastly, animals inhabiting the stalactite caverns of 
Austria, which are all quite blind. These last show remarkable 
adaptations for climbing over the pillars of stalagmite, in 
which occupation they spend most of their time. 
One of the most interesting animals of the Austrian caves is the 
blind newt-like Proteus anguinus. It has small eyes, but they are 
completely covered by the skin, so as to be useless ; their structure 
