96 ANATOMY OP THE ANOPLA. 



a longitudinal direction. Towards the tip the texture becomes denser in transverse section 

 (Plate XVIII, fig. 7), and the pigmentary matter increases, especially just within the pale external 

 layer of the cutis. A section still further back (Plate XVIII, fig. 8) exhibits a less compact arrange- 

 ment, and the pigment is now for the most part grouped into a dorsal and a ventral band. The 

 general stroma consists of radiating and longitudinal fibres, the ends of the latter and the 

 granular matter being often situated in the axils of the diverging series. The pigment anteriorly 

 attains its greatest density immediately beneath the pale external layer of the cutis, diminishing 

 in quantity from this point inwards (Plate XVIII, fig. 9). The snouts of these mobile animals 

 resemble in structure the elaborate arrangements which are sometimes met with in certain organs 

 (such as the tongue) in the higher animals, where extensive and delicate motions are combined 

 with high tactile power. 



To assist in the latter function, there are three papillae on the snout, one of which, from its 

 situation, falls to be described with the opening of the canal for the proboscis. The other two 

 are placed on each side of the central (Plate XIX, fig. 1), but are not always so prominent. Each 

 is furnished with a series of cilia of greater length than those on the general surface, and which 

 extend from the papilla during erection in a radiating or fan-shaped manner. They are probably 

 of great tactile service to the worm. 



The cuticular cells are finer in Lineus lacteus, Mont., MS., and the dorsum is not clouded 

 by the granular pigmentary matter. In Lineus bilineatus the arrangement of the two white 

 dorsal stripes is characteristic, for the pigment is strictly confined to the region corresponding to 

 d" and e in L. gesserensis ; and in transverse section (Plate VI, fig. 7) they appear as two opaque 

 patches with an intervening pale space, bounded externally by the basement-layer of the 

 exterior coat, and internally by the circular muscular fibres. In Borlasia Elizabeth® the cutis in 

 transverse section presents a dappled aspect (Plate XXI, fig. 4) from the intervention of pale 

 patches between the dark-brownish masses. Certain peculiarities are observed in the dermal 

 tissues of Lineus marinus, a species which has been taken as the type of the Nemerteans in this 

 respect by M. de Quatrefages. The external cuticular layer (d, Plate XVIII, figs. 5 and 6) is 

 proportionally thinner than in L. gesserensis. The pigmentary layer (d' , d") is divided by a 

 definite black band (2), and distinctly separated from the first or external longitudinal muscular 

 coat by a curious translucent stratum (3, 3), presenting in cross section (fig. 5) a transversely 

 barred arrangement with linear interruptions, which divide it into numerous and somewhat 

 regular elongated spaces. In longitudinal section (fig. 7), again, this stratum has a wavy aspect, 

 or, if much contracted, presents a series of moniliform streaks. That this layer, however elastic, 

 is not muscular, a glance at the position of the parts in longitudinal section at once demonstrates. 

 It belongs entirely to the dermal elements, and with the interior pigmentary layer corresponds to 

 the region d" in L. gesserensis, which (region) in the larger species attains much greater develop- 

 ment, and becomes distinctly separated from the longitudinal muscular fibres. A similar struc- 

 ture is found in the cutaneous tissues of a typical form of the Anopla brought by Mr. McAndrew 

 from the Gulf of Suez, and also in the Borlasia novce-zealandice of Dr. Baird. 



The skin in many of the Anopla, e.g. Lineus marinus, L. gesserensis, L. sanguineus, L. lacteus, 

 Micrura fusca, M. purpurea, and M. fasciolata, gives a marked acid reaction when tested with 

 litmus-paper. 



