410 The Critics of Evolution, [June, 
to turn upon their sides and to descend to the bottom of the water. 
Here they undergo a metamorphosis, which is a wonderful in- 
stance of the manner in which nature modifies animals and adapts 
them to new conditions. The flounder thus placed at the mercy 
of its environment, begins to change color on the under side 
which becomes whiter from the absence of light, while the upper 
side becomes darker from its continuous action. The eyes were 
originally on opposite sides of the head, as in normal fishes, but 
the eye which was created upon the side which is now under- 
most, gradually moves around and takes its place upon the upper 
side, thus presenting the appearance, familiar to any one who has 
seen the turbot or flounder, of an animal with both eyes on the 
same side of its head. 
They will there find, also, a notice of the transformation of the 
North American axolotl (Siredon) into a completely different 
animal, with which it was not known to have near relationship, 
and already placed in a different genus. They will also see an 
explanation of the manner in which the Alpine salamander has 
probably changed from an egg-bearing to an ovo-viviparous 
animal in places too dry for the production of animals having 
gills in their earlier stages, by causing the eggs to hatch within 
the mother, and the young to pass their gill stage within the fluids 
of her body instead of in water, as do the young of other newts 
or salamanders. 
There is an excellent.lesson in evolution to be found in the his- 
tory of the Sacculina, which is a parasite upon the hermit crab. 
This illustrates the manner in which degradation is brought 
about, for this is often as striking a process of evolution as is 
advancement to higher forms. This Sacculina, as it is found on 
hermit crabs, is a sort of cylindrical mass with a bundle of roots 
growing from one side; sense it has none, limbs none, organs 
none, and hardly the vestige of organs and only the faintest traces 
of mouth and intestines. It is an embryo but not far enough 
advanced to show what it is to be. Listen to its history. This 
structureless lump began life as a little barnacle crab, swimming 
in the ocean, having a symmetrical body, three pairs of legs and 
one eye, and bearing a close resemblance to the embryos of all 
crabs in this state, which is called the “nauplius stage,” or that 
first to develop out of the egg. Very soon our nauplius barnacle 
leaves off roving and attaches himself to the soft hind parts of a 
