The Cubomedusæ

by Franklin Story Conant

One is strongly tempted by the foregoing comparison to speculate a little as to whether the reproductive organs of the Cubomedusæ, which lie in the stomach pockets and are generally supposed to be endodermal, may not bear some closer relation to those of the Trachomedusæ, which lie “in the course of” the radial canals (Lang’s Text-book) and by common consent are ectodermal. And while we are being led by facts such as those just mentioned above to wonder just a little whether after all the position of the Cubomedusæ among the Acraspeda is so firmly assured—doubting some, yet in the frame of mind of one who “fears a doubt as wrong”—the velarium suggests itself as another point in question. Haeckel does not hesitate to state emphatically that the velarium of the Cubomedusæ and the velum of the Craspedote medusæ are only analogous, but the reasons that he gives (sie sind unabhängig von einander entstanden, und ihre Structur ist zwar ähnlich, aber keineswegs identisch; namentlich das Verhalten zum Nervenring ist wesentlich verschieden: System, p. 426) somehow do not produce so much impression upon one as the very velum-like appearance of the velarium itself. The origin from the fusion of marginal lobes is not as yet a matter of observation, and the relation to the nerve ring is not essentially different from that of the velum to the lower (i. e. inner) nerve ring in the Craspedotæ. The four frenula and the diverticula from the gastro-vascular system seem to be the chief differences in structure after all, and these Haeckel evidently did not think worth mentioning. This speculation, as to the possible relation of the Cubomedusæ to such forms of the veiled medusæ as Liriope, though it may be very tempting, is scarcely fruitful enough to repay much effort on the part of either reader or writer. The whole subject must remain uncertain until the facts of the development of the Cubomedusæ are known.

If the structure of the vascular lamellæ of the internal system has been made clear, the appearances of the vertical and horizontal components in the figures will be understood without much further explanation. The four vertical strips in the interradii (ivl) have been already referred to in the figures of the cross-sections of both Charybdea and Tripedalia. In the longitudinal sections of the two jelly-fish through the interradii, the vertical lamellæ are cut throughout their entire length from stomach to connecting canals (Figs. [5-20], ivl). The horizontal cross-pieces at the tops of the vertical lamellæ also appear in several of the figures. [Fig. 36] represents the appearance that would be given by a longitudinal section taken through any portion of the upper part of the bell except in the interradii, or in the perradii, through the gastric ostia. The horizontal vascular lamella (hvl) is shown connecting the endoderm of the stomach (ens) with that of the stomach pocket (enp). In a longitudinal section directly through an interradius ([Fig. 5 or 20]) the horizontal lamella is cut just at the point where it joins the vertical, so that the two are not differentiated. In a section through the region of a perradius ([Fig. 4 or 19]) the horizontal lamella is of course not cut, since the section passes through the gastric ostium, whose existence is conditional upon fusion not having taken place between the endodermal surfaces.

The first figure in each of the series of cross-sections (Figs. [6] and [21]) also shows the horizontal vascular lamella, cut across slantingly twice in each quadrant as it passes between the gelatine of the ex- and of the subumbrella to connect the epithelium of the stomach with that of the stomach pocket. The fact that more of the lamella does not appear in such a cross-section only shows that its course is not perfectly horizontal.

The region in which the same lamella lies is indicated in the surface view of the top of the bell of Charybdea ([Fig. 2]) by the bent line hvl in each quadrant. The figure manifests the appropriateness of Claus’s name for the horizontal lamella—“bogenförmige Verwachsungs-Streifen.” Haeckel calls the same structures “Pylorus-Klappen,” and in his account of Charybdea Murrayana in the Challenger Report, speaking of the three divisions of the stomach (buccal, central and basal) which he traces upwards from the stalked forms of Scyphomedusæ, he says: “The central stomach in this Charybdea, as in most Charybdea, is joined to the basal stomach, as the pyloric stricture between the two is not developed and only faintly indicated by the slightly projecting pyloric valves.” Again, in speaking of the valves of the gastric ostia, he says: “These four perradial ‘pouch valves’ alternate with the interradial pyloric valves.” It is difficult to understand, however, how the “bogenförmige Verwachsungs-Streifen” of Claus, which are undoubtedly the same structures as those which I have called the horizontal lamellæ, and are only strips of endodermal fusion, can be “projecting pyloric valves,” or indeed can properly be spoken of as valves at all. Possibly Haeckel was not quite able to understand Claus’s description, and in his desire to find something in the stomach of Charybdea which would serve to set off a central from a basal part, such as is found in the Lucernaridæ, hit upon Claus’s “Verwachsungs-Streifen.” I have elsewhere given it as my opinion that in such of the Cubomedusæ as I have studied there is no structure in evidence that would properly serve to mark a limit between a basal and a central portion of the stomach.

We have next to describe the marginal system. The vascular lamellæ mentioned above in every case connected endoderm of one cavity with endoderm of another; those of the margin have the noteworthy difference that they run from endoderms of some part of the gastro-vascular system to ectoderm of the surface. The outermost cells of the endodermal lamellæ make direct connection with the ectodermal cells, without the usual intervention of a layer of gelatine.

The marginal lamella of Charybdea lies, as the name implies, just on the bell margin where the edge is curving round into the velarium. All around the whole circumference of the bell it is found (in Charybdea) at this same horizontal bend, except in the eight principal radii, where the tentacles and the sensory clubs have brought about modifications. In any place except these a vertical section through the margin will show the marginal lamella connecting the endoderm of the marginal pocket with the ectoderms of the surface, as represented by vlm in [Fig. 38], which is a vertical section through the sensory niche a little to one side of the perradial axis.

In the interradii the marginal lamella undergoes modifications due to the fact that the bases of the pedalia are situated a little upwards from the exact margin, and that the lamella follows the outline of the bases. [Fig. 1] shows one of the interradial corners of the bell margin looked at directly from the surface, so that the curved outline of the junction of the base of the pedalium with the exumbrella is seen. The trace made by the lamella where it meets the surface ectoderm follows this outline. The lamella is also shown in the vertical section through the interradius ([Fig. 5 or 20], vlm), where it is seen running from the connecting canals (cc), which joins the two adjacent marginal pockets, upwards and outwards to meet the surface ectoderm. Its course from canal to surface is not in a direct line, but curved with the concavity upwards. Hence, in cross-sections at certain levels through the interradial corner it is met more than once and gives rise to appearances that seem at first sight too complicated for it to be just the same structure as the simple marginal lamella described above. That it is the same, and that the complication is only due to the insertion of the pedalia above the margin, can be determined by following through a series of cross-sections, the essential ones of which, as I hope, are given in [Figs. 40-43]. The levels of these are shown on [Fig. 5] by the letters w, x, y and z, respectively. [Fig. 40] shows the lamella cut but once, just below its highest part. The section is above the level of the connecting canal and hence still shows the vertical interradial lamella ivl. [Fig. 41], at the next lower level (x), shows the same portion of the lamella intersected a little nearer the interior, while the junction with the endoderm of the connecting canal is shown still further inside. [Fig. 42] is at level y, just through the bend of the loop, so that in part of its course the lamella is cut almost horizontally, i. e. in its own plane. [Fig. 43] finally shows the lamella as it appears below the level of the connecting canal, cut twice, each portion joining endoderm of marginal pocket with ectoderm of surface. It thus bears exactly the same relations that it had when we first met it in [Fig. 38] (vlm), except that here in [Fig. 43] one finds that a cross-section cuts it at right angles instead of a vertical as in [Fig. 38], as a result of its being pushed upwards from its former position on the margin by the insertion of the pedalium above the margin.

The vascular lamella of the sensory niche has already been alluded to as part of the marginal system, and brief reference has been made to it in the section on the sensory clubs. Like the rest of the marginal lamella, it connects endoderm with ectoderm. The line that its fusion with the ectoderm traces on the surface frames in a shield-shaped area at the bottom of the sensory niche, which is seen in the drawing of the outlines of the niche, [Fig. 44] (vls). This lamella was observed by Claus, and was figured by him both in surface view and in cross-section through the niche. Apparently, however, he omitted vertical sections through the niche, so that he supposed that the outline traced by the lamella was not continuous above, i. e. over the stalk of the sensory club (’78, Fig. 41; text, p. 28). That the outline is closed above, though masked in surface view by the roof of the sensory niche, is seen at once in vertical sections, such as [Figs. 37 and 38], one of which is directly through the perradius, the other a little to one side. Both show the vascular lamella of the sensory niche (vls) intersected twice, above and below the sensory club, and completely cutting off the exumbrella from any share in the bottom (or inner wall) of the sensory niche. [Fig. 39], which is a cross-section through the upper part of the niche, and is essentially like the similar figure of Claus, shows in like manner that the bottom of the sensory niche belongs to the subumbrella. H. V. Wilson was the first to point out, in his unpublished notes, that the lamella of the niche is complete all round.

In the adult structure of Charybdea and Tripedalia the lamella of the niche is connected with that of the margin by a vertical strip of endodermal fusion that does not come to the surface like the rest of the marginal system, but remains just internal to the gelatine of the exumbrella, connecting the two adjacent marginal pockets. In the cross-sections of Charybdea it is seen in [Fig. 16] (vlc); in those of Tripedalia it is seen in [Figs. 28 and 29]. In vertical section it is found in Figs. [4], [19] and [37]. In [Fig. 44], which represents the bell margin and velarium of Tripedalia arranged as if the velarium were vertical and pendant from the margin (instead of suspended by the frenulum so as to be at right angles to the vertical plane), the connecting lamella is shown as a dotted line (vlc)—dotted because it does not come to the surface—joining the lamella of the niche with that of the margin (vlm).

The same figure ([No. 44]) shows a characteristic difference between the marginal lamella of Tripedalia and that of Charybdea. While in Charybdea, as Claus points out, the marginal lamella keeps at one level, just a little above the bell margin, all the way round (except where disturbed by the special modifications of the tentacles and the sensory clubs), and never descends into the velarium, in Tripedalia on the other hand it describes a sinuous course, following the outlines of the marginal pockets, as is indicated in the figure by the light parallel line vlm. The course as it would be seen in a surface view is obscured just at each side of the interradius by the overhanging of the bases of the two lateral pedalia. This is why the lamella is not indicated at these points in the diagram. The course is seen to lie almost wholly on the velarium, that is, in the figure below the line which represents the bell margin proper, the line at which the angle comes when the velarium is in its normal position, horizontal to the vertical side of the bell.