REPORT ON THE PENNATULIDA. 147 



These conclusions agree completely with what we have said 

 already concerning Faniculina, in which, as in Pennatiila, development 

 of the polypes appears to pi'oceed from the dorsal towards the ventral 

 surface, and from below upwards, the ventral polypes being always the 

 biggest and oldest, and the dorsal ones the smallest and youngest. 



The zooids, or rudimentary asexual individuals, cover as already 

 noticed the whole ventral surface of the rachis excepting the median 

 groove, which is often barely perceptible in the upper half of the Pen. 

 They also extend up the sides of the rachis, between the bases of the 

 leaves (Fig. 3 e), and form on the dorsal surface little clusters between 

 each pair of leaves. The zooids exactly reverse the arrangement we 

 have found to hold among the polypes, the ventral zooids being the 

 smallest, and the dorsal clusters invariably the largest. In the case 

 of the younger leaves these dorsal zooids are not much smaller than 

 the youngest, or most dorsal polypes, and it is possible that they may 

 develope into them, as we have supposed to occur in Funiculina. We 

 have not, however, had sufficient material at our disposal to enable us 

 to determine this point. 



i. — Anatomy of the Polypes. 



The polypes of Pennatuhi agree in all essential features with those 

 of FunicuUna already described,* the differences, which are of merely 

 secondary importance, being due mainly to the fusion of the polj'pes 

 to form leaves in Pennatuhi. 



The structure of the polypes is shown in Figs. 3, 4, and 5 ; Fig. 3 

 representing a whole leaf, with its component polypes ; Fig. 4, a 

 longitudinal section through one polype taken along the line AA in 

 Fig. 3 vertically to the surface of the leaf ; whilst Fig. 5 represents a 

 transverse section of the leaf along the line BB in Fig. 3, the section 

 cutting the six most ventrally-situated poh'pes of the leaf at different 

 points of their length. 



We propose now to consider the several parts of the polype, 

 taking them in the same order as in the description of Funiculina. 



a. The Body-wall consists, as in FunicuUna, of a firm gelatinous 

 mesoderm (Fig. 5 .r), clothed on its outer and inner surfaces by 

 ectoderm, w, and endoderm, //, respectively. The mesoderm, and 

 therefore the body-wall of which it forms the greater part of the 

 substance, is thinner than in Funiculina, from which it differs further 

 in being very thickly beset with the characteristic red calcareous 

 spicules (Figs. 3, 4, 5 (). These spicules are of very various sizes and 

 placed in different directions, though usually with their long axes more 

 or less parallel to that of the polypes ; their shape and other characters 

 will be described further on. 



The partition walls between the several polypes of a leaf have the 

 same structure as the external body-wall, but are very much thinner, 

 the mesoderm being hardly thicker than the cellular endoderm 



* Supra, pp. 25—36. 



