TEGUMENTAEY SYSTEM — TOUCH. 



and likewise of the dermis enters into the primary elements in the formation 

 of a scale. In some cases in which the. scales are large they push through 

 the epidermal layer, becoming partly free, as seen in many ctenoid forms, as 

 perches and sparoids. 



TOUCH. 



Special organs of touch are developed in fishes in several different manners. 

 Some, as carps, have highly sensitive' barb els arranged around their- mouths ; 

 they are likewise well seen in siluroids or sheat-fishes, which as a rule live in 

 muddy waters, and have mostly to obtain food by means of the delicacy of 

 their power of sensation, while their organs of vision are but little developed 

 (page xxviii). Or these organs may possess more solid bases, but have still a 

 similar function, as in the sub-man dibular or hyoid barbels of the red mullet 

 (plate viii), or the modified maxilla of some sheat-fishes, or even the. fin- 

 rays themselves, which for this purpose have occasionally long filamentous 

 terminations, as seen in the John Doree (plate xlviii), or be modified into 

 organs, not only for progression but likewise for sensation, as in the free 

 pectoral rays of gurnards (plates xxiito xxviii). Or these tactile organs may 

 be more essentially cutaneous, as the filaments on the snout of the sole 

 (plate cvi), or perhaps more distinctly visible on the lemon sole (plate cvii) ; 

 while somewhat similar but larger filaments are found on the bodies of some 

 fish, as the angler (plate xxix) . Even papilla3 as round the naouths or on the 

 lips are highly sensitive, and as has been shown by Leydig and others they 

 are abundantly supplied with nerves. 



The lateral-line* consists of a series of tubes along either side of the bodies 

 of fish (page vii, fig. 1) and is often known as the mucif erous system ; but 

 although from it mucous is excreted, it is essentially an organ for sensation, 

 and as such is variously modified. It is continued on to the head, where the 

 tubes are largely developed in many families, as the scia)noid and cod-fishes ; 

 or may form several canals, as seen in the Arctic chimasra (plate cli). In 

 osseous fishes the inside of the canal of the lateral-line is lined with epithelial 

 cells, often differing in form in different families. Into this canal nerves 

 raitiify, and either terminate in an expansion or anastomose with each other, 

 as in Plagiostomes. The simple tubes of Lorenzini are restricted to Plagio- 

 stomes, where their presence, due to their black colour, render them so 

 apparent in the skate (vol. ii, p. 337, pi. clxvi), they open at the surface of 

 the skin, do not anastomose one with another, are supplied with nerves, and 

 filled with a thick gelatinous substance, aad may be tactile organs. ■ 



* Dercum proposes tp term it " the lateral sensory apparatus. 



