THE MAMMOTH CAVE AND ITS INHABITANTS. 751 
less rapidity, and become finally fixed and habitual. Prof. Hagen 
has seen afemale of Cambarus Bartonii from Mammoth Cave, 
“« with the eyes well developed,” and a specimen was also found 
by Mr. Cooke. Prof. Hagen remarks that “ C. pellucidus is the 
most aberrant species of the genus. The eyes are atrophied, 
smaller at the base, conical, instead of cylindrical and elongated, 
as in the other species. The cornea exists, but is small, cireular, 
and not faceted ; the optic fibres and the dark-colored pigments 
surrounding them in all other spe- 
cies are not developed.” It seems 
difficult for one to imagine that our 
blind craw fish was created sud- 
denly, without the intervention of 
secondary laws, for there are the 
eyes more perfect in the young than Fig. 133. 
the adult, thus pointing back to an- J 
cestors unlike the species now ex- 
isting. e can now understand, 
why embryologists are anxiously 
studying the embryology of animals 
to see what organs or characteristics 
are inherited, and what originate de 
novo, thus building up genealogies, 
and forming almost a new depart- 
ment of science: comparative em- 
bryology in its truest and widest 
Caxcidotea stygia (side view). 
e. 
Of all the animals found in caves, 
either in this country or Europe, 
perhaps the most strange and unex- 
pected is the little creature of which 
we now speak. It is an Isopod crus- 
tacean, of which the pill bugs or sow bugs are examples. A true 
species of pill bug (Titanethes albus Schiédte) inhabits the caves of 
Carniolia, and it is easy to believe that one of the numerous species 
of this group may have become isolated in these caves and modi- 
fied into its present form. So also with the blind Niphargus sty- 
gius of Europe, allied to the fresh water Gammarus so abundant 
in pools of fresh water. We can also imagine how a species of 
Asellus, a fresh water Isopod, could represent the Idoteidz in our 
Cecidotea stygia (dorsal view). 
