VIUaULARIA MIKAlill^IS. 55 



canals. At their outer ends the radial canals can sometimes be traced 

 into continuity with a system of very fine canals with no distinct 

 epitheliiil lininf», which branch in an irrcfjnlar way throuf;h the meso- 

 derm of the rachis, and communicate both with the polype cavities and 

 with the main canals of the rachis, and which clearly correspond to the 

 fine nutrient canals traversing the mesoderm of both Funiculina and 

 Pennatuhi. 



This system of ventral or radial canals has been described cai-efully 

 by Kolliker in the genus Halisceptnim,* in which its main characters 

 and relations appear to be the same as in Virgularia, though differing 

 in some points of detail. We are in much doubt concerning the 

 function of these canals. Kolliker says they are to be regarded as a 

 modification of the nutrient canals, and possibly subserving some 

 special function. The epithelium lining them has a very glandular 

 appearance, and, bearing in mind their position at the points of com- 

 munication between, on the one hand, the fine canal system which 

 penetrates the mesoderm in all directions, and is in communication 

 with the polype cavities, and, on the other hand, the main canal 

 system of the rachis and stalk, it has occurred to us that they may 

 very possibly be excretory organs and act as kidneys, separating eifete 

 matters from the fluid in the fine nutrient canals, and discharging it 

 into the main canal system. This view derives some slight support 

 from the fact that in more than one case we have seen small collections 

 of debris over the orifices from the radial canals into the main canal, 

 which were apparently being discharged from the former into the latter. 



The chief difficulty in assigning this or indeed any other important 

 function to this system of canals, lies in the fact that they are found only 

 in certain members of the Pennatulida. They are present in Virgularia 

 and Halisceptrum ; but Pennatula and Funiculina have no trace of them. 

 They can have nothing to do with the ova, for they are far too small 

 to admit them ; neither, so far as our observations go, do ova ever 

 occur in the main ventral canal, though, as we have seen, they do pass 

 into the lateral canals. 



2.— The Stem.— 



The stem or calcai-eous axis of the rachis and stalk (Figs. 2, 3, 4, 5, 

 and 6, c), is cylindrical, firmly calcified, and brittle. According to 

 Dalyell it contains as inuch as 85 per cent, of mineral matter, chiefly 

 carbonate and phosphate of lime, and only 15 per cent, of animal 

 matter. 



Not only does the stem of Virgularia differ from that of Pennatula 

 or Funiculina in its greater brittleness, but the proportions at various 

 parts of its length are also very different. Both in Pennatula and 

 Funiculina the stem is thickest at or just above the junction of the stalk 

 and rachis, from which pomt it tapers both upwards and downwards, 

 ending at both ends in fine, imperfectly calcified, and very flexible points 



* Kolliker : op. cit, pp. 169, 170, 



