374 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



layer of the pale exterior coat, and internally by the circular muscular fibres. In 

 transverse section the cutis of Meckelia annulata contains rather small cells 

 (Plate XIV. fig. 11), which retain much of their ordinary shape after mounting. 

 The characteristic opaque white dorsal and lateral pigment-stripes pass through- 

 out the entire thickness of this tissue, while the white touches on the sides that 

 apparently correspond with the openings of some of the ovaries or sperm-sacs do 

 not traverse the entire thickness, but lie towards its inner border. 



The skin in many of the Borlasians, e.g., Lineus longissimus, Borlasia olivacea, 

 B. octoculata, B. lactea, Micmra {Stylus) purpurea and M. fasciolata, gives a 

 marked acid reaction when tested with litmus-paper. 



Muscular Coats. — The longitudinal muscular coat (e), which is incorporated 

 with the former cutaneous layer at its commencement, is thick and powerful, 

 and has a well-marked fasciculated aspect in transverse section. At the sides of 

 the mouth, where this coat attains great development, and forms a strong lateral 

 support, there is a very pretty radiated or somewhat arborescent arrangement of 

 the interfascicular substance on transverse section (Plate XI. fig. 1, 2). Such a 

 condition would permit great stretching in all directions without actual separation 

 of the muscular bundles, and is thus eminently adapted for the functions of the 

 parts. The intimate connection of the outer fibres of this layer with the adjoin- 

 ing coat is well brought out in some superficial longitudinal sections of the body, 

 which show the outer bundles of fibres quite separated from each other by rows 

 of pigment and other cells and granules, — the whole having a curiously streaked 

 appearance. Anteriorly this longitudinal layer becomes lost in the tissues of the 

 snout. The next coat (e') consists of a series of circular muscular fibres of con- 

 siderable thickness, and it is between this and the former that the nerve-trunks 

 are situated. It passes by the sides of the ganglia, and appears to merge into 

 the wall of the passage for the proboscis in front of these organs. In Cerebra- 

 tulus bilineatus this coat is decidedly thicker than usual, a condition which may 

 be connected with the somewhat rounder form of the body generally in the species. 

 Within the last-mentioned coat is a layer (e") of longitudinal muscular fibres, 

 similar in structure to the corresponding stratum in Ommatoplea. Like the 

 former the fibres pass the ganglia to become connected with the muscular channel 

 for the proboscis in the snout. 



Certain peculiarities are observable in the dermal tissues of the large Lineus 

 fongissimus (Borlasia anglise, Quatref.), and since this species has been taken as 

 the type of the Nemerteans by M. de Quatrefages and others, it is necessary to 

 enter somewhat minutely into the anatomy of the parts, as shown in the trans- 

 verse and longitudinal sections (Plate XL figs. 6 and 7). The external cuticular 

 layer (d) is proportionally thinner than in the common species. The pigmentary 

 layer \d'\ d") is divided by a definite black band (2), and is distinctly separated 

 from the first or external longitudinal muscular layer by a curious translucent 



