HYDROIDA II 



153 



evinces a remarkably high power of variability in the thickness of its chitinose parts, a point which 

 has been noted by Ssemundsson (1902 p. 57) and later by myself (1909 p. 190); this variation, more- 

 over, also affects the diaphragm in a peculiar manner. In finely built specimens, the diaphragm is of 

 the same structure as in typical Laomedea species, that is to say, it consists merely of a thin basal 

 plate spread out below the base of the polyp; in colonies of coarser build, the chitinose thickening 

 makes itself especially apparent in the adthecal part of the diaphragm, only approaching the margin 

 at a much later stage, so that in longitudinal hydrotheca sections, the diaphragm appears triangular, 

 supported on a broad base resting upon the hydrotheca wall. The diaphragm here, however, is in 

 no wise more "complex" than before, and does not particularly resemble the low, ring-shaped wall 

 thickening in Campanularia, Taking all this in connection with the sympodial development of the 

 colonies, we can have no doubt we have here to deal with a typical Laomedea. 



The figure of Laomedea flexuosa mentioned above as reproduced by Nutting after Kuhn 

 (1909 Taf. 17, fig. 7) shows the typical Laomedea diaphragm. A typical picture of what we find in 

 Campanularia is shown in fig. 1, PI. I. 



Gen. Campanularia (Lamarck). 



The colonies are stolonial, creeping or upright rhizocaulomes. The hydrothecse have no true 

 diaphragm, but are divided by an inner thickening of the wall, more or less restricted in extent, into 

 a large outer cavitv and a smaller basal. The polyp can withdraw entirely into the radially symme- 

 trical hydrotheca; it has a club-shaped proboscis and homogeneous gastrai endoderm. 



Quite exceptionally we find, among certain species, a slight approach to the formation of up- 

 right colonies based upon a sympodial mode of ramification, so that one stalk may carry a single 

 secondarv lateral stalk with hvdrotheca. This must be regarded as the earliest indication of the typi- 

 cal svmpodial colonies which characterise Laomedea. The Campanularia species lack true diaphragm, 

 but have a ring-shaped thickening of the wall (plate I fig. 1) which forms the upper limit of the 

 basal cavity, and furnishes, in its superior part, the point of attachment for the basal supporting 

 lamella of the polvp, which is fixed to the thickened part by a wreath of small chitinose bodies. The 

 chitinose thickening may be broad and not very sharply defined, or more sharply defined and nar- 

 rower, in which latter case it assumes the character of an incipient diaphragm, but also in this case 

 it is restricted to a low ridge. 



Campanularia volubilis (Linne) Schweigger. 

 IJ58 Sertularia volubilis, Linne, Systema natune, Ed. 10, p. 811. 

 1820 Campanularia volubilis. Schweigger, Handbuch der Naturgeschichte, p. 425. 



Creeping colonies, from the stolons of which proceed the hydrotheca; stalks, these being as a 

 rule distinctlv coiled in a spiral throughout their entire length; more rarely, the spiral may be less 

 marked in certain parts, or throughout the entire length of the stalk. The stalk invariably termin- 

 ates in a distinct ball-shaped joint under the hvdrotheca. The hydrotheca; themselves are not very 



20 



The Ingolf-Expedition. V. 7. 



