SO 



debris of the other superficial cells, forms the slimy coating of the fish's skin. There 

 are no special glands connected with the skin of the sole. 



In the outermost layers of the fibrous derma, immediately beneath the epidermis, 

 are situated the pigment cells or chromatophores. Some chromatophores are also 

 found in a deeper position, in the fibrous tissue which lies between the deeper parts of 

 the scales, but no pigment is found below the level of the skin to which the anterior 

 edges of the scales reach. The epidermis and the thin subjacent layer of the derma, 

 which contains the chromatophores, are continued over the exposed portions of the 

 scales, with the exception of the longest most posterior spines of the scales : these pierce 

 through the skin and epidermis and project beyond the latter. 



The appearance of a longitudinal section through the dermal tube of the lateral line, 

 magnified 40 times, is shown in Fig. 6, Plate XIV. In other parts of the skin muscles 

 are of course found below the derma, but the dermal tube of the lateral line lies 

 directly above the connective tissue partition between the dorsal and ventral lateral 

 muscles, and the connective tissue of this partition passes directly into the skin. 

 The fibrous tissue of this partition contains large spaces occupied by loose 

 reticular tissue the meshes of which are large and filled during life with lymph ; 

 this tissue is seen in the lowest part of the figure. The figure includes one whole scale 

 of the lateral line and parts of two others ; the three pores, p,p,p, corresponding to 

 these scales are seen leading into the dermal tube. The section passes longitudinally 

 through the centre of the dermal tube and therefore the roof of the tunnel formed by 

 each scale is seen above the dermal tube, and the floor below it. The dermal tube is 

 seen bending down to pass through the hole in one scale to enter the tunnel of the 

 scale behind it ; beyond the hole in the floor of the scale a branch of the dermal tube 

 passes backwards to open on the surface at the external pore. The dermal tube is 

 lined by an epithelium which is only separated from the surface of the scales by 

 a very thin fibrous membrane. This epithelium is continuous with the epidermis at 

 the external pores, but differs much from the epidermis in character. It is of very 

 slight thickness, consisting only of two or three layers of cells. The lowest layer 

 consists of small undifferentiated cells which grow and multiply, continually 

 replenishing the outer layers. Nearly all these outer cells are globular and vesicular ; 

 that is they form hollow capsules, doubtless containing mucus. During life the dermal 

 tube contains mucus, which is the product of this epithelium. But at certain places 

 this epithelium contains sense-organs, consisting of portions of the epithelium which 

 have an entirely different structure and function. The cells of the sense-organs are not 

 secretory but sensory, and they are connected with nerve fibrils. One of these sense- 

 organs, as seen in longitudinal section, is shown at s.o, in PI. XIV, 6. It is situated on 

 the inner wall of the dermal tube, and lies on the floor of the tunnel of a scale a little 

 in front of the hole through which the dermal tube passes to the next scale. At a point 

 near the anterior and deep border of the scale containing the sense-organ there is a 

 small aperture in the scale through which a nerve passes from the skin below the scale. 



