PLATE XIII. 



Fig. 1. Cerebratulus comigafu^, M'Int. Transverse section through part of the superior brain-lobes and 

 dorsal brain commissure. Part of the fibrous core (h) is represented; its continuation into the 

 fibres of the commissure (f.co) being distinctly noticed on the left side. On the right this 

 connection is only visible a few sections further. The bulk of the brain-lobe is seen to con- 

 sist of nerve-cells of different sizes (n.cl); from these a cephalic nerve (en) is seen to emerge 

 on the left, whereas this cellular coating is also continued over the commissure, and there 

 forms the starting point (m) for the longitudinal dorso-median medullary nerve. 



Fig. 2. Cerebratuhis corrwjatus, M'Int. Horizontal section of the same specimen through the medullary 

 nerve m. In this section only a portion of the cylindrical nerve-plexus (npJ), of which the 

 medullary nerve is only the median thickening, is visible. The transverse nerve-tracts tr.n, 

 paired and metamerical, being thicker than the plexus, are cut along a more considerable 

 surface and thus stand out as separate nerves. The openings in the plexus give passage 

 to radial, transverse, contractile fibres, as is specially indicated in fig. 4, rf. 



Fig. 3. Cerebratulus corrugatiis, M'Int. Portion of a horizontal section through the ventral extension of 

 the nerve-plexus, n, the nerve-tissue of the plexus with nuclei of nerve-cells, and bundles 

 of radial fibres rf. piercing it. 



Fig. i. Cereliratuhis corrui/atus, il'Int. Portion of the same section as fig. 2, more highly magnified. 

 /;, the tissue of the nerve-plexus with delicate fibres and distinct nuclei of nerve-ceUs, also 

 visible in the medullary nerve 7n ; rf, the bundles of radial, contractile fibres. 



Fig. 5. Cerehratulus romigatus, M'Int. Ventral view of the head and long mouth with rugose lips of 

 large specimen. Natural size. 



Fig. 6. Cerebrattdus ccrrrugatus, M'Int. Eadial strip out of a transverse section in the oesophageal region. 

 Jsg, the outer glandular layer of the integument (with " Schleimstabchenzellen "); h, the 

 secondary basement membrane below this ; JJcm, the longitudinal and circular muscle-fibres 

 peculiar to the integument ; Jdg, the deep glandular layer just below these ; B, the 

 primary basement membrane of the integument radially traversed by contractile fibres 

 (rf) and nerve-bundles (n) going towards the integument ; y, the outer longitudinal 

 muscles ; pi, the nerve-plexus with fibres and cells, pierced by the radial contractile 

 bundles rf; /3, the circular muscular layer; a, the inner longitudinal muscular layer; cos, the 

 circumffisopliageal intercommunicating blood-lacunse, clothed by a cellular endothelium ; 

 into, the cesophageal musculature ; nv, nerve-tissue in the oesophageal wall ; ^>a/), an 

 (Tsophageal papilla with deeper glandular and superficial ciliated cell-layers. 



Figs. 7, 8. Cerebratuhis rnacroren, n. sp. Two sections through the principal nephridial duct of a 

 specimen from Japan. Contracted (fig. 7) and distended (fig. 8). 



Fig. 9. Cerebratulus rnacroren, n. sp. Anterior tubuliferous proliferation of the nephridia. a, /3, mus- 

 cular layers as in fig. 6 ; Ne2), nephridian tubules applied against the ^vall of the circuin- 

 oesophageal blood-lacuna ; Oe, outline of resophagus wall. 



