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 the view that the papilla has been withdrawn, is the very distinct flask- 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 present. 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 bo 

 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 papillae thus buried, and never in Lepidogobius. Leydig 

 ('79, p. 25) has suggested the probability of the contractility of the 

 cellular elements of the papilla) 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, 1 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 papilla; are well 



