4 The Blind Cave Fishes and their Allies. [January, 



age examples from the largest sub-maxillary row measured .01 

 in height by half that width. I found no projecting filament, 

 however, in any of the cups, such as is described and figured by 

 Professor Wyman in the papers of Mr. Putnam already cited. 

 The interior structure of the papillae also differs greatly from that 

 of Amblyopsis, as the latter is represented by Professor Wyman. 

 In Amblyopsis, according to that eminent anatomist, each papilla 

 is supplied with a nerve fiber which terminates in a short, flexible 

 filament springing from the middle of the concavity in the tip of 

 the papilla. In the Chologaster each papilla is likewise pene- 

 trated by a nerve fiber, which is very easily traced, even without 

 the help of reagents, because of the black pigment in the neu- 

 rilemma, but this nerve passes to an epidermal " end organ" pre- 

 cisely similar in structure to those minute bodies found abun- 

 dantly embedded in the skin of the head of young fishes, and 

 belonging to the same general class as those sensory structures 

 which occupy the lateral line. 



This "end organ," or " nerve button," which fills the interior 

 of the distal third or half of the papilla, is a nearly globular mass 

 of cells, partly various modifications of the columnar, and partly 

 spindle-shaped or spherical, each of the latter with a filamentous 

 prolongation at one or both ends. The nerve fiber of the papilla 

 passes, without division, to the inner end of the cell-cluster, 

 where its fibrils appear to continue into the filamentous processes 

 of the cells. Having no fresh material for the osmic acid treat- 

 ment, I could not positively demonstrate the terminations of the 

 fibrils. These are evidently simple examples of that class of 

 structures to which a supposed "sixth sense " of fishes and am- 

 phibians has been assigned, and by which these animals are be- 

 lieved to appreciate motions of the water and wave lengths lon- 

 ger than those of sound. 



The importance of well developed structures of this character 

 to fishes without the use of the sense of sight, is very manifest. 

 The close general resemblance between these organs and those 

 described for the blind fishes, taken in connection with their simi- 

 lar situation,- arrangement and apparent use, is probably sufficient 

 evidence that the two kinds are homologous. 1 



1 Is it not possible that the specimens of Amblyopsis studied by Professor Wyman 

 were not perfectly preserved, and had lost more or less of their superficial epithel- 

 ium, and with this the "nerve buttons" from the tips of their papilla;? Some color 



