REPORT ON THE PENNATULIDA. 245 



the whole width of the ventral surface of the racliis. In this respect 

 Virpiihtria agrees with both the other genera. 



The Zooids in Vir<iuJaria are exceedingly rudimentary ; more so 

 even than iu Fennatula. They form small pit-like depressions on the 

 sides of the rachis, placed iu somewhat oblique rows at the bases of 

 the leaves (Fig. 5 e). 



4. — Anatomi/ of the FoJijpes. — 



The polypes of Virfiularia as might be expected are essentially 

 similar to those of FanicitUna or Fennatula ; resembling, owing to their 

 fusion into leaves, those of the latter rather more closely than the 

 former genus. 



The structure of the adult polypes is shown in Figs. 5 and 7, the 

 former figure representing the seven polypes composing a leaf in their 

 natural relation to one another and to the rachis ; while the latter figure 

 represents transverse sections of three polypes taken at different parts 

 of their length, the upper section passing through the stomach and 

 the base of the tentacles ; the middle section through the mesenterial 

 filaments immediately below the stomach ; and the bottom section 

 passing through the lower part of the body cavity, not far from the 

 rachis. 



Taking the component parts of the polypes in the same order as iu 

 the other two genera, we have to deal first with 



a. The Body-ioall : consisting of a firm gelatinous mesoderm (Fig. 

 7, x) covered on its outer surface by the ectoderm, lu ; and on its inner 

 by the eudoderm, y. Ectoderm and endoderm each consist of a single 

 layer of epithelial cells, while the mesoderm is traversed by branching 

 nucleated cells, and also by fine tubular channels, in connection with 

 those of the rachis. 



This mesoderm is tough, and has considerable powers of resistance 

 to re-agents ; it gives their definite shape to the polypes ; and in speci- 

 mens of Virgularia taken from a haddock's stomach at Scarborough 

 iu a partially digested condition, the mesoderm alone had escaped, 

 ectoderm, endoderm, and all the internal organs being iu most cases 

 dissolved out completely. 



At their lower ends the polype cavities (Fig. 5) are, as iu Fennatula, 

 separated by only very thin partitions from the main dorsal and 

 lateral canals of the rachis ; while the curious system of radial 

 canals, (Fig. 5, vc) as already noticed, communicates with the 

 body cavity of the most ventral polype of the leaf. 



We have not noticed any perforations iu the walls separating the 

 several polypes of a leaf from one another, such as are described and 

 figured by KoUiker as occurring in HalLiceptrum and other genera. 



The body-walls of Virgularia, as already noticed, contain no 

 spicules ; differing in this respect most markedly from those of 

 Fennatula. 



b. The Calyx. — This forms (Fig. 6, g), a wall surrounding the 

 tentacles when these are either partially or wholly retracted. It 



