384' DR W. CARMICHAEL M'INTOSH ON THE STRUCTURE OF THE 



Dalyell) makes his error still more apparent, for he says, " Toute la trompe se 

 meut librement dans la cavite intestinale." * Prof. Keferstein gives a small 

 figure f of a transverse section of the organ in Cerebratulus marginatus turned 

 inside out ; but, though he indicates the lozenge-shaped space formed by the 

 crossing of the fibres, it is misplaced on one side, and the entire figure is too 

 indistinct for reference. 



Digestive System. — The mouth in Borlasia olivacea 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 represented in Plate X. 

 fig. 1, w. Certain broad pale lines radiate from the lips of the fissure (which lines 

 in dark specimens are generally pale), an arrangement which led Dr G. Johnston 

 into the error of considering it a nerve-ganglion and branches. These radiating 

 lines or folds are due to the same structural cause as those in the ciliated oeso- 

 phageal region of Ommatoplea — viz., prominent longitudinal rugae 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. In Borlasia lactea, Mont. MS., the mouth is 

 situated very far back, leaving a long space between it and the ganglia. In 

 Cerebratulus, again, the aperture is a longitudinal slit, somewhat less marked 

 than in Borlasia. The mouth leads into a great ciliated oesophageal chamber (/), 

 which commences anteriorly as a cul-de-sac behind the ganglia and cephalic sacs, 

 and nearly closing in by its anterior wall the vascular lacunae there, while it may 

 be said to terminate posteriorly at a distinct incurving of its Avail, by becoming 

 continuous with the digestive cavity-proper. In the transverse section (Plate XI. 

 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 large space is occupied by the pro- 

 boscidian sheath {a), and the great lacunae (s, s), and indications of some other 

 vascular meshes are seen at the sides The lips of the mouth (w) curve inwards, 

 and gradually merge into the ciliated glandular texture of the cavity. A little 

 further back the glandular substance becomes confined to the inner surface of 

 the body-wall (though actually not closely applied thereto), leaving a large 

 central space. In full perfection the chamber and glandular texture are seen in 

 Plate XIII. fig. 6. The minute structure of the wall of this portion of the 

 digestive cavity is similar to that of the ciliated oesophageal region in Omma- 

 toplea, being composed of a thick layer of granular gland-cells and basement- 

 substance, raised here and there into prominent rugae, and richly ciliated on the 



* Op. cAt. p. 17. f Op. cit. taf. vii. fig. 5. 



