THE SENSE-OEGANS AND PERCEPTION OP FISHES. 233 



Amongst the flat-fishes this elliptical series of plates arranged 

 along a single axis is found in the genera Rhombus (turbot and 

 brill) and Arnoglossus (merry sole and megrim). In a very large 

 turbot the number of chief folds was thirty. 



(4) In all the species of Pleuronedes^ examined^ as well as in 

 Hippoglossus vulgaris (the halibut), an entirely different arrangement 

 is found. In these fishes {v. fig. 2) only one row of olfactory plates 

 is present. The plates thus arranged in a single series lie in a direc- 

 tion parallel to the long axis of the body, and not transversely to it, 

 as the majority of them do in other types. The arrangement in 

 Solea has already been described. 



In the pollack and rockling, and probably in all fishes, if the 

 whole olfactory organ be destroyed with acid, the skin heals over 

 the part, but the special epithelium and the nostrils are not repro- 

 duced j but in a conger in which the olfactory organ had been only 

 partially destroyed, the plates of epithelium were found to be 

 regenerating from the edges of the olfactory tissue which had re- 

 mained undestroyed. 



Sense-organs of the Mouth and Skin. 



The scales and skin generally of fishes are supplied with remark- 

 able sense-organs, which resemble the taste-buds of higher forms. 

 These organs have been fully described and figured by Merkel in 

 his monograph, Ueher die Endigungen der sensihlen Nerven in der 

 Haut der Wirhelthiere (Kostock, 1880). In the course of these 

 investigations a good deal of the ground covered by Merkel's work 

 has been gone over, and to it there is little to add. It will be 

 profitable, however, to mention those facts which specially concern 

 the purposes of the present inquiry, and to describe the characters 

 of some of these organs in forms which have not been investigated 

 by Merkel. 



Such organs consist essentially of clusters of long cells arranged 

 together to form a bulb- shaped body, of which the apex is not 

 covered by cuticle, but projects on the surface of the skin. The 

 base of the bulb may be in contact with the basement-membrane of 

 the skin, or may be separated from it by several layers of cells of 

 the lower layer of the skin (cf. figs. 13 and 14). Into this base a nerve 

 enters. Such an organ may be large and visible to the naked eye, 

 as in the pharyngeal walls of most fishes, or it may consist of only 

 a few such cells and be extremely minute. These minute '' taste- 



* Viz. P.flatessa (the plaice), P.Jlesus (the flounder), P. limanda (the dab), P. micrO' 

 cephalus (the lemon sole of the enst-coast fisheries). 



