84 THE VOYAGE OF H.M.S. CHALLENGER. 



The brain of the Schizonemertea was fully discussed in a former publication (ix). The 

 Challenger Schizonemertea all conform to this type, with the additional facts alluded to 

 above in connection with the medullary nerve. The difference in the size of the ganglion 

 cells in different regions of the brain, as it appears in PI. XII. figs. 7, 8, and PI. XIII. 

 fig. 1, is much more marked in certain species of Cerebratulus than in others. The 

 larger sized nerve-cells appear to be principally peripherally and anteriorly situated ; that 

 they are absent, or less numerous, in certain other species, may be seen by comparing 

 PL XII. fig. 1, with the above mentioned figures. The relative distribution of fibrous 

 and cellular nerve-matter in the brain need not be any further described in detail after 

 our foregoing description and figures of Eupolia. The size and shape of the posterior 

 lobe is, however, somewhat diflerent in the Schizonemertea. This will be obvious by com- 

 paring pi. i. fig. 1 of the treatise referred to (ix) with our present figures of Eupolia. 



Not having been able to study any of the Challenger species alive, we should have to 

 be content with reconstruction from section series, if I were to enter more fuUy into the 

 discussion of the respective difi"erences, and for that reason I wish to restrict myself 

 to these general remarks. 



One other point connected with the posterior lobe and its ciliated duct deserves 

 special mention, viz. , the observation I was able to make that the duct which leads from the 

 bottom of the cejihalic slits into the nerve-tissue of the posterior brain-lobe (inside the 

 brain-lobe it very generally has an S-shaped, and, at the same time, a spiral twist, thus 

 being very often as in PL XIV. fig. 6, cut in three places, all in one section), and which is 

 clothed in the neighbourhood of its external opening with an epithelium directly con- 

 tinous with, and similar to, that of the outer surface, not only shows certain difierences 

 in its epithelium, as we pass further inwards (PL XIV. fig. 11), but also ofiers certain 

 complications, which we have now to consider. These complications very distinctly con- 

 cern the participation of deeper cellular layers of the integument. As indicated by gl in 

 PL XIV. fig. 11, these deeper layers segregate and form a ring-shaped or cushion-shaped 

 addendum to the simple epithelial tube. It must be doubted whether they communi- 

 cate with the exterior, as do the deeper glands of the integument, although this 

 deserves special attention, because of the glandular significance which must be attached, 

 according to Dewoltezky (ll), to the strongly refractive cells present on the posterior 

 surface of the hinder brain-lobe {cf. p. 94). The epithelium has undergone still more con- 

 siderable alteration when it passes inside the posterior brain-lobe. Its nuclei are distinct 

 (PL XIV. figs. 6, 7, 8), but instead of direct cell partitions we may observe a fine striation 

 vertical to the axis of the ciliated canal (fig. 8). This feature, known to former observers 

 (IX, figs. 35, 36), may here be more especially alluded to, because in Hoplonemertea 

 (PL XIV. fig. 10) we find that the discharge of glandular products from the deeper gland- 

 cells takes place between the interstices of this striated region. This discharge into the 

 lumen of the canal is a point that is put beyond doubt by numerous Challenger sections. 



