86 General Notes. [ January, 
After describing the hitherto unknown peculiarities of the brain 
of Asellus and isopod Crustacea in general, the histological ele- 
ments, and the optic lobes, nerves, and eyes, the brain of the eye- 
less forms was then described. Cecidotzea in its external form is 
a somewhat dwarfed Asellus, with the body, however, much 
longer and slenderer than in the eyed forms, and with slenderer 
appendages. It is not usually totally eyeless, since in some in- 
dividuals a rudimentary eye, in the shape of a minute black 
speck, is seen on each side of the head; the spot varying in size 
in different individuals. 
From the examination of numerous microscopic sections it 
appears that the eyeless Cecidoteza differs from the eyed form 
(Asellus) in the complete loss of the optic ganglia, the optic 
nerves, besides the almost and sometimes nearly total loss of 
the pigment cells and lenses. As regards the other parts of the 
brain, no differences were observed; the proportions of the brain 
and the histological structure had remained unchanged in the 
eyeless forms. Besides the atrophy of the optic ganglia and 
nerves, the pigment mass forming the retina and also the lenses 
exist in a very rudimentary condition. In one specimen the 
number of lenses was reduced to two, and the lenses themselves 
many times smaller than in the eye of the normal Asellus. 
The steps taken in the degeneration or degradation of the eyes, 
the result of living in perpetual darkness, seem to be these: 
1. The total and nearly or quite simultaneous loss by disuse of 
the optic ganglia and nerves, 
2. Breaking down of the retinal cells. 
3. The last step being, as seen in the totally eyeless forms, the 
disappearance of the lens and retina. 
That these modifications in the eye of the Cecidotza are the 
result of disuse and the loss of the power of vision from the ab- 
sence of light seems well established; and this, with the many | 
parallel facts in the structure of other cave Crustacea, as well as 
insects, arachnids, and worms, seemed to the author to be due to 
the action of two factors : (a) change in the environment and (6) 
heredity. Thus one is led by a study of these instances, in a 
sphere where there is little if any occasion for the exercise of a 
struggle for existence between the organisms, to a modified 
form of Lamarckianism in order to account for the origination of 
these forms, rather than the theory of natural selection, or pure 
Darwinism, as such.— A, S, Packard. 
On THE MORPHOLOGY OF THE Tarsus IN THE MAMMALS.— 
While occupied with an extended paper on the limb-skeleton of 
the vertebrates, I have obtained some new views on the homology 
of the tarsal elements in the Mammalia. For some time I have 
been puzzled by a bone in the tarsus of different mammals, 
which has always been considered a “ sesamoid.” 
Flower (Osteol. of Mamm., 2d edit., p. 317) says of this bone: 
