or all the eye muscles are present; in Typhlichthys nothing is left of them. [A] Archiv f. Entwickelungsmechanik, viii, pp. 545-617, Plates XI-XV. Scleral cartilages are not present in Chologaster or Typhlichthys; in Troglichthys they are very prominent, sometimes _several times as long as the eye_. While there is no pigment left in Typhlichthys, there is in Troglichthys. The eye in the former is about 0.168 millimetre in diameter, while the entire eye of the latter is but about 0.050 millimetre, or less than one third the diameter, and less than one ninth the bulk. The entire eye of Troglichthys is smaller than many single cells, and I shall be pardoned for not going into the details of its structure here. [Illustration: FIG. 5.--Three views of the head of an _Amblyopsis_, prepared to show the tactile ridges.] [Illustration: FIG. 6.--Snout of _Chologaster papilliferus_, to show the tactile ridges.] THE TACTILE ORGANS.--The tactile organs are among the most important in the consideration of the blind forms. Their minute structure will form the basis of a separate paper. The prominent tactile organs about the head of Amblyopsis have been mentioned by nearly every writer, and they have been figured by Putnam-Wyman[B] and Leidig,[C] but the figures of the distribution of the ridges are worthless. The description of Professor Forbes[D] of Chologaster papilliferus is the only systematic enumeration of the ridges that has appeared. The accompanying figures, drawn by me with the _camera lucida_, and verified and copied by Mr. U. O. Cox, give the exact extent and position of the ridges in Amblyopsis and Chologaster papilliferus. It will be seen that in the number and distribution of the tactile area the two forms agree very closely, the eyed form having the same number and distribution of ridges or rows that the blind forms have. In Chologaster papilliferus most of the ridges are much less prominent than in the blind species, being sunk into the skin. About the nose and chin, however, the ridges are as prominent as in the other species. In the small Chologaster cornutus there are no distinct ridges at all, the tactile organs being arranged as in other species of fishes. In specimens of the same size the papillæ are not more prominent in papilliferus than in cornutus. It is only in the oldest of papilliferus that the papillæ become prominent. The number of individual papillæ in each tactile ridge differs considerably with age (size), so that an exact comparison between the large Amblyopsis and the much smaller species of Chologaster and Typhlichthys can not be made. From a number of counts made by Professor Cox I take the liberty of giving the following: Ridge No. 6 contains, in Chologaster papilliferus, six organs; in Typhlichthys, eleven; in two specimens of Amblyopsis, respectively eighty-three and one hundred and six inches long, twelve and twenty. [B] American Naturalist, 1872, Plate II, Figs. 1 and 2.