44 ANATOMY OF THE ENOPLA. 



have escaped, and thus greater prominence is given to the hyaline intercellular substance. It is 

 granular throughout, especially towards the outer and inner edges. In many transverse sections 

 pressure of the thin glass cover causes a change in each of the preparations, so that the more 

 cellular appearance of the outer edge is partly clue to the fact that the texture is seen from with- 

 out, 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, particularly in those much 

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

 wrinkling of the skin (Plate XVI, fig. 2) ; but such crenations clo not affect the muscular layers, 

 and have no connection with the diverticula of the digestive chamber, or. as supposed by some of 

 the older authors, with true annuli. A thin longitudinal section from the surface of the integu- 

 ment shows a series of meshes with crenated edges, the size of the spaces being variable. In 

 Nemertes Neesii and N. gracilis, the cells or areolae of the skin are smaller than in^. lactifloreus ; 

 the former having much dark pigment in its cutaneous textures dorsally ; and the surface in N. 

 gracilis sometimes presenting the appearance of microscopic mosaic work, from the beauty and 

 fineness of its areolae . In a young specimen, apparently of Amphiporus spectabilis} transverse 

 section demonstrates that while most of the longitudinal pigment-belts on the dorsum are in 

 the cutaneous tissues outside the circular (external) muscular layer, two very well-marked 

 stripes lie quite within both the latter and the longitudinal muscular coat. They are placed 

 on each side of the arch of the proboscidian sheath, and doubtless are the cause of the darker 

 appearance which characterizes the median bands when viewed from the dorsum. Similarly, in 

 Tetrastemma Hobertianm the rows of pigment, constituting the two brown stripes on the dorsum, 

 are at the inner border of the cutis — touching the circular muscular coat ; while the median white 

 stripe is placed within the longitudinal layer, exactly over the proboscidian canal. The reddish- 

 brown pigment in the Zetlandic variety of Tetrastemma Candida is also chiefly developed towards 

 the inner margin of the cutis. Much brownish colouring matter is produced in the skin of the 

 pale Ainphiporidse after prolonged confinement, and thus fresh examples from the rocks are always 

 necessary for the more minute investigations. This is well marked in ProsorJiOchmus, where the 

 pigment-cells and granules form a kind of mesh work by the looping of the rows. 



The chief function of this elaborate glandular arrangement is, no doubt, the secretion of the 

 abundant mucus, so characteristic of these animals, and which is often of a most tenacious descrip- 

 tion. I have seen a specimen of A. lactifloreus rapidly form an investment by this means, when 

 placed in a vessel containing a little sand ; and whether the sand-particles simply adhered to the 

 gelatinous mucus by accident or otherwise, the animal took fall advantage of the protection. The 

 silky sheaths of Tetrastemma dorsalis are also examples of this cutaneous secretion. The same 

 habit of tube-forming is extensively followed by the Amphiporidae of our southern shores, apparently 

 to protect themselves from the increased danger of desiccation. On placing a living specimen on a 

 glass slip, and causing it to emit some mucus, the secretion proves to be .a minutely granular 

 fluid, intermingled with a few larger corpuscles ; and it is produced by the entire surface of the 

 skin, both in this group and in the Planariae, not by any special portion thereof, as supposed 

 by Mr. Darwin in the latter animals. One of the densest tubes is formed by Nemertes 

 carcinopliila, Kolliker, (Plate VI, fig. 5, and more highly magnified in fig. 6), and this has an 



1 This specimen was kindly sent, with other forms, by Mrs. Collings, of Sark. 



