OCR Text |
Show 514 DR. HUBRECHT ON A NEW PENNATULID. [May 19, septa as we proceed towards the rhachis, a transverse connecting septum, however, keeping up a direct continuity, and being placed perpendicularly to the two parallel ones, and at the same time symmetrically. The internal space is consequently now divided into four spaces instead of two, two lateral spaces having made their appearance in addition to the dorsal and ventral (Plate X X X I . fig 12, and woodcut, p. 515, fig. 2). When we examine the figures in K61- liker's monograph (' Anatomisch-systematische Beschreibung der Al-cyonaiien, I. Pennatuliden,' plate x. fig. 78 ; plate xiv. figs. 107-113 ; plate xxi. fig. 180 ; plate xxiii. fig. 212) of sections through the stems of different genera of Pennatulids, we find that there, too, a similar arrangement of the septa and the spaces obtains, and that towards the inferior extremity of the stem the spaces are also reduced to two. One remarkable difference to be noticed in our specimen is this, that whereas in the other Pennatulids au axis of more or less considerable size and massive consistency appears and is situated in the median vertical septum above alluded to (cf. Kolliker's figs. 78, 108, 110, 212), such an axis is entirely absent in Echinoptilum, no trace of it being found either in the stem, the lower part of the rhachis, or its upper portion. The septum in which it is always developed is there, however, as was just noticed. W e must now observe that in the rhachis the dorsal, ventral, and lateral spaces which we have been describing for the stem, and which are here so symmetrically placed, are none the less present throughout the whole of the rhachis, but are here reduced in size by the development of spaces exteriorly to them, in which the polyps will partly be lodged. Fig. 13 gives a satisfactory representation of this arrangement. It is a section in the lower third of the rhachis, and shows us the two parallel septa with the perpendicular one between them, situated in the axis of the rhachis, and at the same time the four spaces which they help to enclose, uninterruptedly continued from the stem into the rhachis, their bulk being, however, not inconsiderably reduced. At the top of the rhachis they disappear, transverse sections showing that they only reach so far as close to the top, but that at the very extremity only the additional spaces ps belonging to the terminal polyp-cells are present; this would to a certain extent bring out another point of comparison between the septa here discussed and those carrying the axis in other Pennatulids, the latter structure being known not to attain the topmost extremity of the poly-parium, but to stop short close to the top of the rhachis. The accompanying woodcut (p. 515) exemplifies diagrammatically the arrangement of the primitive spaces in transverse sections of different regions of the polyparium. For comparison fig. 4 is copied from Kolliker. Returning now to the base of the stem, we note in longitudinal sections (fig. 9) that here the short median, ventral, and subterminal furrow, already mentioned above when reviewing the external characters of the specimen, is indeed a depression in the integument, and that at the bottom of this depression a flat expansion of the sclerenchyma separates the cavities of the hollow stem from the |