60 W. A. HERDMAN. 



corpuscles are seen. Fig. 20 shows a small portion of tlie 

 mesoderm more highly magnified, to show the network 

 of connective tissue and the small blood-lacunce in the 

 meshes. 



At the bases of the cerata these large ceratal sinuses are 

 continued into the body, and their communication can be 

 traced in sections with the anterior and posterior dorso-lateral 

 veins (fig. 17, d. l. v.), which open directly into the auricle. 

 The junction between the ceratal sinus and the dorso-lateral 

 vein is effected by means of a narrow transversely running 

 branch, and from this point the ceratal sinus is continued 

 ventrally through the mesoderm of the body-wall outside 

 the " liver," and may be called the lateral sinus (fig. 17). It 

 is with the upper part of these lateral sinuses that the prolonga- 

 tions from the liver come in some places into close proximity, 

 and so may have given rise in dissections to the appearance of 

 a direct continuity between the liver and the blood-spaces in 

 the cerata. 



The cerata contain also bands of muscle-fibres, mostly lon- 

 gitudinal in direction, nerves, pigmented connective tissue, 

 forming branched masses and ramifying tlireads of a rich 

 brownish colour, and finally masses of large distinctly nucleated 

 cells, lying in meshes of fibrous connective tissue (see fig. 21). 

 These occur chiefly in the smaller branches of the cerata, and 

 are possibly mucus-secreting glands ; they resemble the small 

 groups of gland-cells seen under the ectoderm in the cerata of 

 some species of Eolis (see fig. 37). The contrast in structure 

 between transverse sections of the cerata of Dendronotus and 

 of Eolis is seen by comparing figs. 18 and 34 or 35. 



DOTO. 



In the genus Do to there are no true branchiae; the rhino- 

 phores are large with simple filiform distal ends, but having 

 their bases surrounded by large funnel-shaped sheaths. The 

 cerata form a row along each side of the back (fig. 22) ; they 

 are very large and complicated, being swollen, tuberculated, 

 usually brightly coloured, and forming the most conspicuous 



