308 DR W. CARMICHAEL M'INTOSH ON THE STRUCTURE OF THE 



The skin is somewhat opaque, and presents a cellular or cellulo -granular 

 appearance. In a small living specimen it is represented as a transparent object 

 in Plate IV. fig. 8, the entire field being definitely covered with glandular cells, 

 and the reddish pigment grouped here and there in varying and irregular granular 

 masses. On snipping a portion of skin from an adult living specimen, and 

 placing it under moderate pressure (Plate IV. fig. 3), it presents the aspect of a 

 series of ovate or spathulate cells, which contain soft and minutely granular con- 

 tents, interspersed with large clear masses of mucus (like oil) of a somewhat 

 similar figure, the latter becoming more numerous as the pressure increases. 

 There are also numerous pigment and other granules scattered over the field. 

 Changes, however, rapidly ensue in this delicate texture, as noted by M. de 

 Quatrefages, both in this group and in Planaria, and the masses of mucus pass 

 rapidly to the nearest free border and there accumulate, the granular contents of 

 the cells following a similar course, but not coalescing. Some of these free globules 

 are shown in Plate IV. fig. 7, a being the granular masses, and b a group of 

 mucous globules like oil. The former structures, though very mobile, are less so 

 than the latter. A transparent gelatinous basis-substance, often of a reticulated 

 aspect, remains after the extrusion of the foregoing elements from the skin. 



When a transverse section is made of an animal hardened in spirit and 

 mounted in chloride of calcium, the appearance of the dermal textures (Plate IV. 

 fig. 2) is as follows: — In rapidly prepared and newly mounted specimens, a 

 structureless film is sometimes observed to separate from the exterior of the skin, 

 as indicated by the double line at the edge of the figure. Chloride of calcium 

 would seem to destroy this delicate structure, as after a time it becomes indis- 

 tinct, and I have not seen it in those hardened in chromic acid. The cellular 

 cutis {a) is found to have undergone an alteration, being streaked perpendicularly, 

 an appearance due to the collapsed state of the areolae and cells, whose contents to 

 a greater or less degree have escaped, and thus given greater prominence to the 

 hyaline intercellular substance. It is granular throughout, and rather more so 

 towards the outer and inner edges. In most of the transverse sections, the 

 pressure of the cover has caused flattening of the skin, so that the increased 

 cellular appearance of the outer edge is partly due to the fact that the texture 

 is seen from the surface, and not laterally. Towards the inner edge, the skin in 

 this state sometimes assumes a crenate aspect, and adjoins a pale and structureless 

 basis-layer (b), which separates it from the subjacent muscular walls of the body. 

 In longitudinal sections of the textures, especially in those much hardened or 

 slightly exposed to air, spurious annulations are caused by the folding inwards or 

 wrinkling of the skin, but such crenations do not affect the muscular layers, and 

 have no connection with the segmentation of the digestive chamber, or true 

 annuli. A thin longitudinal section from the surface of the skin shows a series 

 of meshes with crenated edges, the size of the spaces being variable. In Omnia- 



