64 REPORT ON THE PENNATULIDA. 



moi*e careful examiuation than we have had the opportunity of making 

 would show that the ventral polypes actually appear slightly before 

 the dorsal ones, which would completely prove our case. We shall 

 find further on additional evidence that Vir;iulana is less primitive 

 than either of the two other allied genera, Ftmiculina or Pennatula. 



The dorsal polypes of each pair of leaves are (as shown in Figs. 3 

 and 5) separated from one another by a very short interval at their 

 bases, while the most ventral polypes (Figs. 4 and o) are separated by 

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

 Virrjularia agrees with both the other genera. 



The Zooids in Viriiularia are exceedingly rudimentary ; more so 

 even than in Pennatula. They form small pit-like depressions on the 

 sides of the rachis, placed in somewhat obluj[ue rows at the bases of 

 the leaves (Fig. 5 c). 



4. — Anatomy of the Polypes. — 



The polypes of Virgularia as might be expected are essentially 

 similar to those of Funiciduia or Pennatula ; 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 in 

 the other two genera, we have to deal first with 



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

 7, .r) covered on its outer surface by the ectoderm, ir ; and on its inner 

 by the endoderm, 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 

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

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

 dissolved out completely. 



At their lower ends the polype cavities (Fig. 5) are, as in Pennatula, 

 separated by only very thin partitions from the main dorsal and 

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

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

 body cavity of the most ventral polype of the leaf. 



