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



thatwhicli is continued into the lateral nerve-stems, i.e., an incipient distinction between 

 a pair of upper and a pair of lower lobes, respectively limited by the dorsal and ventral 

 brain commissure ; the whole forming a ring round the proboscis and its sheath. A 

 side view of the brain of Carinina — reconstructed from a series of sections — is given 

 in the accompanying woodcut, in which the very thin dorsal commissure is not 

 indicated. A comparison with figs. 4 and 7 of PI. V. will at once show the relation of this 

 stage of diflPerentiation to that to which Eiqoolia has attained. In the Schizonemertea 

 the separation between upper and posterior lobes is more marked still than in Eupolia 

 (PL XIV. fig. 6) ; in the Hoplonemertea they are definitely separated, and only con- 

 nected by one or more nerve-strands (PI. IX. fig. 10), their situation being then some- 

 times behind, and even sometimes before the rest of the brain. 



The ciliated canal penetrating into the posterior lobe of Carinina is simple (not 

 divided in two as in certain Hoplonemertea), and provided with a high, ciliated epithe- 

 lium of its own. It is figured in figs. 1 to 3 of PI. VI. Certain glandular cells, gl. hr, are 

 seen in this same figure to have become specially developed in connection with this 

 posterior lobe and its ciliated canal. Similar glandular cells also form a characteristic 

 feature of the posterior brain-lobes of Schizonemertea and Hoplonemertea. In Carinina 

 it is evident that these glandular cells are derivatives, or at least morphological equiva- 

 lents, of the deeper glands Gi, of the integument. 



The nerve- cells themselves, out of which the brain is built up, still undoubtedly 

 belong to the integument, and it is exceedingly difficult, if not impossible, to draw a 

 sharp distinction between the outermost brain-cells and the surrounding integument-cells. 

 In the figures just cited this difference has been artificially very much accentuated in order 

 to bring out more distinctly the outline of the brain ; for the same reason, the integu- 

 ment in this figure was on purpose not fully worked up. 



The inner core of the brain is fibrous, so is the core of the longitudinal stems, where, 

 however, the attempt at a distinction between nerve-cells and cells of the surrounding 

 integument is equally hazardous (PL III. fig. 8). This fibrous core is in direct continuity 

 with the nerve-plexus, that spreads out in the deeper integumentary layers. 



A vagus nerve passing from the lower portion of the brain on both sides towards the 

 oesophagus is also distinct in Carinina (PL VI. fig. 1, iVv).' The passage of contractile 

 fibres through the brain-substance is unmistakable, though less evident than in Carinella. 



Passing on to the description of the nerve-centres of Eupolia, we immediately recognise 

 the difference resulting from the fact that here the brain is imbedded inside the muscular 

 layers, as is also the case in all Schizonemertea. 



Our description of the brain of Eupolia maybe based upon the figures of PI. V., which 

 were obtained not de visu, but by reconstruction from a series of sections.^ Figs. 1-4 



1 For the making of these and many other series of sections, and for assistance in the reconstruction above alluded to, I 

 am indebted to the kindness of Dr. Gudemans, my former assistant, now director of the Zoological Garden at the Hague. 



