86 BULLETIN OF THE 
the papilla, but the inverted hopper-shaped outline which the inner sur- 
face of the epidermis shows immediately under the papilla in most cases 
where the latter reaches out freely to the surface (as in Figures 24 
and 26), is here entirely obliterated. Another fact that seems to favor 
the view that the papilla has been withdrawn, is the very distinct flask- 
shaped excavation in the summit of the papilla itself, seen in Figure 23 
(fos.), while in the sections represented in the other two figures no such 
excavations are preseut.. A natural explanation for this would seem to 
be that, on being drawn in, the middle portion of the papilla with the 
sense cells had been more depressed than the mantel cells. This may be 
the true explanation, but in one instance I have found the excavation in 
the papilla, even though the papilla itself protrudes through the epider- 
mis, even more distinctly than in Figures 24 and 26; yet it should be 
mentioned that in this exceptional instance the papilla is considerably 
narrower in proportion to its length than those shown in the figures 
just referred to, or than they usually are. I have searched in vain for 
muscle fibres that could bring about such a withdrawal, and have no 
other evidence than that presented that it takes place; nor have I 
often found the papille thus buried, and never in Lepidogobius. Leydig 
(79, p. 25) has suggested the probability of the contractility of the 
cellular elements of the papillae as the cause of an apparently similar 
condition in Acerina cernua. 
A word should perhaps be spoken at this point on the possibility 
of the loss of sight being compensated by a higher development of the 
organs of hearing or smell. This subject lies outside of the purpose of 
the present paper, and I have given only superficial attention to it. 
The ears examined in dissected specimens mounted in glycerine do not 
appear unusually large. The minute structure I have not examined ; 
but from this morphological evidence, taken with the fact that all my 
efforts to get from my single living specimen responses to sounds of 
various kinds were unavailing, I am inclined to believe that the sense 
of hearing is not largely developed. 
My sections of the snout show the olfactory epithelium to be very 
well developed, though apparently not more so than in other bony 
fishes, and certainly not so highly as in some of the long-tailed am- 
phibia that I have examined. 
What we know about the compensatory development of the tactile 
organs in other vertebrates with rudimentary eyes may be summed up 
as follows. It is well known from the writings of Tellkampf, Wyman, 
Leydig, Putnam, Wright, and others, that the tactile papille are well 
