NERVOUS SYSTEM. 109 



Sir J. G. Dalyell, whose untiring scrutiny of the habits of such animals is worthy of all praise, 

 saw a Lineus (his Gordius gesserensis) feeding by the ventral slit, which he therefore correctly 

 termed the mouth. Dr. Johnston in his 6 Catalogue' observes : — " There is another and much 

 larger aperture in front, behind and underneath the head. Long mistaken for the mouth, this 

 has been usually described of late as genital, but the orifice is doubtful." He terms the 

 alimentary canal the general cavity of the body. M. van Beneden does not demonstrate that the 

 so-called biliary elements are simply constituents of the wall of the digestive cavity, and not 

 special caeca attached to the sides of the canal. In Lineus bilineatus (his Cerebratulus CErstedii) 

 he states that the nutritive chamber is divided into three compartments — the first short, and 

 corresponding to the oesophagus ; the second twice or thrice the length of the former, and 

 representing the stomach ; the third extending to the posterior extremity of the worm and con- 

 stricted at regular intervals, and equivalent to the intestine. I have not yet noticed this in 

 the British examples, which agree with the typical Lineidce in the structure of the organ, 

 although the external aperture or mouth is somewhat smaller. Prof. Keferstein's description of 

 the cavity as applied to Linens, though brief, is good, and his criticism of Van Beneden's view, in 

 regard to the " liver " in the same group, fair. 



7. Nervous System. 



The cephalic ganglia or central organs form two large and conspicuous pale red masses 

 situated a short distance behind the snout of the worm (Plate XIX, fig. 1). They differ in 

 shape, as seen under slight pressure, from the same organs in the Enopla, each half being 

 narrower and more elongated, so as to cause the entire arrangement to have the appearance of a 

 horseshoe-magnet. In some specimens, instead of being more deeply tinted than the rest of the 

 cephalic tissues, they are paler, on account of the deep red coloration of the latter ; while in others 

 they can scarcely be distinguished under the dense blackish-green coating of cutaneous pigment. 

 They are surrounded by the usual fibres of the region, besides the proper sheath of the ganglia. 

 The inferior commissure, often of a deep red hue, is well marked, and placed quite at the front. The 

 curves of the ganglia do not bulge so much forward on each side as in the Enopla, and thus the 

 anterior margin of the system forms a nearly uniform transverse line. The superior commissure 

 is smaller and less distinct ; indeed, it is with difficulty seen in the living animal as a transparent 

 preparation. Each ganglion is composed of a superior and an inferior lobe ; and in minute 

 structure the nervous matter agrees with that in the Enopla. The inferior lobes and commissure 

 rest upon the solid tissues of the snout (Plate XVIII, fig. 9) instead of having the buccal cavity 

 beneath them, as in the latter. On making a transverse section of the ganglionic mass just 

 behind the commissures (Plate XXII, fig. 1), the superior lobe is found to be more rounded 

 than the inferior, and to communicate with its fellow of the opposite side by the superior 

 commissure. The inferior lobes are somewhat ovoid, connected by the great commissure, 

 and give off the lateral nerve-trunks posteriorly. In front the two lobes are soldered 

 together, but towards the posterior part a section is now and then found, which shows the 

 posterior end of the upper lobe separated from the inferior. This severance of the end of the 

 upper lobe is not to be confounded with the free rounded sac which lies close behind, as demon- 

 strated by a section in which the knife has cut the left ganglion somewhat further back than the 



