220 REPORT ON THK PENNATULIDA. 



and these leaves are placed in pairs along the whole length of therachis 

 (Fif^. 1) ; the leaves in the middle of the rachis being further apart, 

 and also rather larger than those at the two ends, but the difference in 

 size being altoiiether insignificant in comparison with what occurs in 

 Pennatttla (cf. PI. III., Fig. 1). 



As in the two other genera, we distinguish in therachis dorsal and 

 ventral surfaces, the latter (Fig. 4) characterised by being bare and 

 free from polypes along its whole length. 



Imbedded in the rachis at the bases of the leaves are the zooids or 

 rudimentary polypes, shown in Fig. 5 e. 



The soft parts of VirpuJaria, contrary to what occurs in Funicvlina 

 and Pennatula, are completely destitute of spicules, calcification being 

 limited to the axial rod or stem. 



Anatomical Descriptiox. 



1. — The Stalk and Rachis. — 



The stalk (Fig. 1, h), as we have seen, is not present in any of the 

 Oban specimens. From the descriptions and figures given by Dalyell,* 

 K6lliker,t and Sars,| it appears that in the few specimens in which it 

 has been preserved the stalk is cylindrical, with a slightly bulbous 

 extremity ; the dilated part, asin /'c;(««fM/rt, having much thinner walls 

 than the rest. 



The stalk is described as of considerable length, very much longer 

 relatively to the whole colony than is the case in Funiculina. Dalyell 

 figures a specimen in which the stalk is StJiu. long ; * and both Dalyell 

 and Kolliker agree in representing the lower end of the stalk as bent 

 up in the manner we have represented in Fig. 1. 



The longitudinal canals of the rachis are prolonged down the stalk, 

 accoi'ding to Kolliker. In its upper part there are four main canals — 

 dorsal, ventral, and two latei'al ; but in the lower part the lateral canals 

 disappear, and the dorsal and ventral alone remain. 



The rachis is widest at its lower end, where the polype leaves are 

 either absent or very rudimentary (Figs. 1 and 6). As we pass upwards 

 and the leaves get bigger, the rachis at first diminishes in width some- 

 what rapidly (Fig. 1), but having attained a diameter of about 0-045in. 

 it preserves this tolerably uniformly along the greater part of its 

 length, tapering again gradually towards the upper end. It is traversed 

 throughout its length by four main longitudinal canals (Figs. 5 and 6 u), 

 one of which is dorsal, one ventral, and two lateral ; these canals, as 

 noticed above, extending down into the stalk. 



The outer surface of the rachis is an epithelial layer forming 

 the ectoderm ; and the main canals have an epithelial endodermal 

 lining. The rest of the substance of the rachis consists of mesoderm : 

 this IS very thin opposite the bases of the leaves, as seen in the 



* Dalyell : op. cit, Plate XLIIL.Fig. 7. 

 + Kolliker : op. cit, Taf. XV., Fig. 104. 

 ; Sars : • Fauna littoralis Norvegire." 



