32 REPORT ON THE PENNATULIDA. 



continued change still going on, evidently with the object of regaining 

 its original form, the fluid seeming to oscillate from one end to the 

 other. The above changes took place in the first twenty minutes from 

 the time of capture." 



With regard to the second point, which can, of course, only be 

 settled by direct observatious on living specimens, we will only 

 remark here that Mr. Goode's observation that at the moment of 

 capture the proportions of the stalk were those we have described and 

 figured froin spirit specimens, is important testimony in favour 

 of these proportions being the normal ones ; and further, that 

 Panceri's suggestion appears to us to be of much weight, and that 

 it is quite possible that it also gives the clue to Sir John 

 Dalyell's statement concerning the " nocturnal habits " of Peii- 

 natula. The bottom of the sea at twenty to forty fathoms 

 depth must be very dark indeed as compared with the surface, and it 

 seems to us very probable that a Pennatula "in a basiu or plate of 

 sea- water " does not expand its polypes fully until the evening, simply 

 because it is only then that the amount of light approxiinates to what 

 it is accustomed to receive in the day time at the bottom of the sea. 



The rachis (Fig 2 «), or axial portion of the feather or polype- 

 bearing part of the Pen, is widest about the junction of its middle 

 and lower thirds. From this point, at which in the female specimen 

 it has a width of 0"29in., it tapers gradually in both directions. Its 

 dorsal surface (Fig. 1) is completely concealed by the polypes, and of 

 the lateral surfaces only small portions are visible between the bases of 

 the leaves. The ventral surface is, however, exposed along its whole 

 length (Figs. 2 and S) ; it is marked by a shallow median longitudinal 

 groove, more pronounced in the female than the male specimen, and 

 is studded all over with the zooids or rudimentary polypes. In colour 

 it contrasts strongly with the stalk, being of a bright red colour, 

 excepting the median groove which is pale yellow. 



The internal structure of the rachis is shown in Fig 3. The central 

 canal, which is of very large size, is divided by the septa shown in 

 this figure into four ; a very large dorsal one, two large lateral ones, 

 and a small ventral one crescentic in transverse section. In the great 

 size of these canals, which do not appear to have been figured hitherto, 

 Pennatula phosphorea contrasts reinarkably with the allied species 

 Pennatula rubra, as described and figured by Kolliker,* in which the 

 dorsal canal is very small, and far removed from the others, which are 

 themselves much smaller than in P. pho^phorca. 



The structure of the wall on the mid-dorsal and on the ventral 

 surfaces is, but for the presence of the zooids, much the same as that 

 of the stalk. A single-layered epidermis covers a thick dermis exceed- 

 ingly closely studded with calcareous spicules, packed 'together if 

 possible even more closely than in the stalk ; beneath the dermis is 



* Kiilliker: Anatomische-systematische Beschi'eibung der Alcyonarieu. 

 Erste Abtheilung ; Die Peiuiatuliden, 1872, Plate VIII., fig. 7-2. 



