106 ANATOMY OF THE ANOPLA. 



Cerebratulus (Erstedii (Z. hilineatus) makes his error still more apparent, for he says <f Toute 1 



trompe se meut librement dans la cavite intestinale." Prof. Keferstein gives a small figure of a 

 transverse section of the organ in Cerebratulus marginatus turned inside out ; but, though he 

 indicates the lozenge-shaped space formed by the intersection of the fibres, it is misplaced on one 

 side, and the entire figure is too indistinct for reference. 



6. The Digestive System. 

 a. Mouth. 



The mouth in Lineus gesserensis is a longitudinal fissure on the ventral surface, situated a 

 short distance behind the ganglia, and varying in size according to the motions of "the animal 

 and the degree of contraction or relaxation. Its ordinary appearance under examination is repre- 

 sented in Plate XIX, fig. 1, w. Certain broad pale lines radiate from the lips of the fissure, an 

 arrangement which led Dr. G. Johnston into the error of considering the mouth a nerve-ganglion 

 and the furrows branches. These radiating lines or folds are due to the same structural cause 

 as in the ciliated oesophageal region of the Enopla— viz., prominent longitudinal ruga? of the 

 thick glandular texture of the organ, which, in this case, permit great dilatation of the parts 

 during ingestion. The number of these rugae varies, as may be observed by a comparison of the 

 figures. When L. gesserensis is killed by immersion in fresh water the mouth frequently presents 

 five or six somewhat triangular folds of the oesophageal structure, which fill up and distend the 

 aperture. The mouth is very conspicuous in Lineus marinus (Plate XVIII, fig. 2). In Lineus 

 lacteus it is situated very far back (Plate XIX, fig. 3), so that a long space intervenes between it 

 and the ganglia ; and there is a marked difference in this respect between the present species 

 and L. sanguineus (Plate XIX, fig. 2). 



In Carinella the oral aperture forms a longitudinal slit, somewhat less conspicuous than in 

 Lineus. In Valencinia lineformis the mouth is quite as distinctly marked as in any example of 

 the latter, and placed far backwards. 



In Cephalothrix the lips of the aperture are frequently thrust outwards in the form of a 

 short funnel, so that the animal resembles an elongated Distoma. Some circular fibres are present 

 round the mouth in this group, and probably exist also in Lineus. 



5. (Esophageal Division. 



The mouth leads into a large ciliated oesophageal chamber (j), which commences anteriorly 

 in the form of a cul-de-sac behind the ganglia and cephalic sacs, and nearly closes by its anterior wall 

 the vascular lacunae there, while it may be said to terminate posteriorly at a distinct incurvation 

 of its wall, by becoming continuous with the digestive cavity proper. In transverse section 

 (Plate XX, fig. 1), the anterior part of this chamber is seen under favourable circumstances as a 

 thickly folded glandular mass (j), with the ventral slit (w) leading quite freely into it. The cavity 

 has not yet attained its full size, and the mouth is severed at its anterior border. Superiorly, a 



