1894.] Subterranean Fauna of North America. 735 
5. The surest evidences of actual degeneration are found, 
first, in the greatly increased quantity of pigment, and secondly, 
in the presence of pigment in regions where none is found in 
the normal eye, as in the hyaloid membrane. 
6. On comparing the eyes of all blind vertebrates that have 
been most carefully studied, all may, in a general way, be said 
to be passing along the same degenerative path. 
7. The eyes of blind vertebrates furnish very little evidence 
on the question whether structures in undergoing actual de- 
generation in ontogeny follow the reverse order of their phylo- 
geny. 
Ritter also states that from the works of European authors 
it is possible to make a detailed comparison of the eyes of 
Typhlogobius with those of Proteus anguinus and of the Euro- 
pean mole, which he proceeds to do. On the whole, the eye of 
Proteus is more rudimentary than that of either Typhlogobius 
or Talpa, the lens being absent in the cave Amphibians. All 
authors, except Semper, are agreed that the optic nerve is 
present in both Proteus and Talpa, but Ritter finds no account 
of it ever having, in either of these animals, a pigment-sheath 
in its passage through the retina, such as occurs in Typhlo- 
gobius. 
III. ÉMBRYOLOGICAL OBSERVATIONS ON THE CONDITION OF THE 
EYES IN THE EMBRYO OR IN THE YOUNG, PROVING THE 
ORIGIN OF THE BLIND OR EYELESS FORMS FROM 
NORMALLY-EYED ANCESTORS. 
No complete observations have, so far as we are aware, been 
made on the embryology of cave animals, nor on that of eye- 
less non-cavernicolous forms, except in the few cases which we 
proceed to mention. In our essay on the Cave Fauna of 
North America (p. 159), we record the fact that in the young 
of the blind crayfish (Orconectes pellucidus), the eyes of the 
young are perceptibly larger in proportion fo the rest of 
the body than in the adult, the young specimen observed 
being about half an inch in length. Previously to this, Dr. 
Tellkampf, in 1844, remarked that “ the eyes are rudimentary 
in the adults, but are larger in the young." Mr. S. Garman 
