VASCULAB SYSTEM. 79 



and often assumes a greyish hue, apparently from the increased development of this tissue, which 

 is exuded as a pale, salmon-coloured, semi-fluid substance on rupture of the body-wall. In 

 JV. gracilis (Plate XIV, fig. 3) the posterior division of the digestive system, viewed from the 

 ventral surface, has a somewhat regularly ramified arrangement, and this is especially evident 

 some time after spawning, when the animal has regained its condition. The colour of the 

 region is deep green by transmitted light, whereas the oesophageal division is brownish. The 

 pinnae in A. pulcher form simple tapering papillae under pressure. In Nemertes carcinophila 

 the cavity is greatly developed, both as regards the rest of the body and its individual structures ; 

 and it also presents a firmer and more consistent aspect than usual on transverse section. The 

 absence of the proboscidian sheath and its contents leaves the central space almost entirely at its 

 disposal. 



Microscopically, the alimentary cavity has, on the whole, less of the regular and firm 

 glandular appearance of the same structure in the Anopla, but is more friable and cellular. Its 

 analogy with that of the higher annelids is also borne out ; for although the biliary matter is not 

 arranged as a distinct organ exterior to the alimentary, it is incorporated therewith, and probably 

 has a similar function. The fluid, however, which bathes the liver in the higher forms (if we 

 suppose that inside the sheath for the proboscis to be the homologue of the former), is here 

 separated by the muscular walls of its special tube ; thus those who imagine, like Mr. 

 Lankester, that the so-called biliary tissue in Clicetogaster and others has some connection with 

 the production of the corpuscles of the perivisceral fluid, find here a fact of interest. I, however, 

 do not see the advantage or necessity of deviating from the very generally applied law, viz. that 

 the fluid itself produces its corpuscles. The large size of the proboscis in the Enopla renders 

 the digestive system very obscure from the dorsal aspect, and it is only when the ventral surface 

 is upturned that a correct knowledge of its relations is obtained. No food has been found in 

 the alimentary cavities of those examined. 



7. Vascular System. 



The circulatory system is composed of three great longitudinal trunks — -one central and two 

 lateral — besides the cephalic arch and anastomotic vessels. Commencing with the central 

 trunk posteriorly (Plate XV, fig. 3, p) in Amphiporus, it is found that the vessel, which in this 

 region is about twice the diameter of the lateral, arises from the point of junction of the last- 

 mentioned, just within the posterior border of the worm. It travels forward beneath the 

 proboscidian chamber in an undulated manner — as usually seen — to the region behind the 

 ganglionic commissures, where it bifurcates (q), a branch passing to either side to join the lateral 

 trunk (r), which bends inwards to meet it. From this point of junction also a single vascular 

 arch (cephalic) proceeds forward into the tissues of the snout (/, same figure, and in Plate X, 

 fig. 2, the latter showing the vessels in transverse section), the pillars of the arch thus meeting 

 the lateral and anastomotic vessels of each side. Prom the same point of union each lateral 

 trunk passes backwards under the nerve-cord to the tail, where it meets its fellow of the opposite 

 side, and gives origin to the single central vessel with which the circuit commenced. The lateral 

 trunks appear to diminish slightly posteriorly. The median vessel does not actually touch the 

 wall of the proboscidian sheath, though transverse sections usually show a close apposition, but is 



