MEDUSAE. I. 



Thus they must undoubtedly be characterised as another transitional form, somewhat further advanced 

 than the corresponding organs in Chroma ton cm a rtibrum. - - In another nearly related species, Chromato- 

 nema hertwigi (Ptychogcna hertwigi Vanhoffen, see below) the same organs are, according to the figure, 

 partly cylindrical, partly spindle-shaped, partly somewhat club-shaped; Vanhoffen calls them "cirri". 



Thus we find, within the Laodiceida, a series of transitional forms of cordyli from cylindrical 

 or spindle-shaped with a distal cluster of nematocysts {Chromatonema rubrum) through spindle-shaped 

 or slightly club-shaped with or without nematocysts, to the fully developed form: actually club-shaped 

 without nematocysts. 



As different points of connection exist between the Laodiceida- and the Tiaridce, as will pre- 

 sently be demonstrated, it is a natural question, whether anything corresponding to cordyli is found 

 among the latter. We will find then, that a single form of Tiarida 

 possesses certain organs, which bear a considerable likeness to the 

 lowest form of cordyli, those of Chromatonema rubrum. The species 

 in question is Tiaranna rotunda (Quoy & Gaimard). 



I deeply regret that my paper on the Anthomedusse and 

 Leptomedusae of the "Michael Sars" Expedition 1910 has not yet 

 been printed, as two species of the interesting genus Tiaranna have pig. i. Part of the bell-margin of Tiaranna 



. . . . . , , . ... rotunda (Quoy & Gaimard). 



been dealt with in that paper ; a reterence to the accounts of these 



V 



species would have facilitated the following discussion on the relation between the Tiarida and the 

 Laodiceida. As especially Tiaranna rotunda is of great interest in this respect, I have thought it 

 better to make use, in this place, of my observations relating to the matter in spite of the fact, that 

 they are destinated for printing in another place. 



The marginal appendages of Tiaranna roiunda (textfig. i) are very much like those 

 of Chromatonema rubrum. Between every successive pair of tentacles in Tiaranna rotunda 

 there are one or two minute appendages like the cordyli of Chromatonema, only they are 

 never cylindrical, but always spindle-shaped, and provided with a tenon-like distal part 

 greatly armoured with nematocysts (textfig. 2). The structure of the cell-layers is exactly 

 as in the cordyli of Chromatonema. Dwarf-tentacles of a similar shape, though more length- 

 ened, are found in Bythotiara. 



Hartlaub (1897) considered cordyli to be juvenile stages of tentacles, and he meant 

 to have observed the development of cordyli into tentacles in Staurophora mertensii. 

 Browne has discussed this question in his paper, Revision of the ... Laodiceida (1907, 

 (miT*'&*Gai- P- 458)- Browne has examined a large number of specimens of Laodicea undulata (early 

 "rmmerou? an< ^ intermediate stages). He is of opinion, that transformation of cordyli into tentacles 

 afhedistai ^ oes not ta ^ e P^ ace normally, though such transformation may happen when the margin 

 of the bell is overcrowded with marginal organs; in such case a cordylus may stand in the 

 way of a developing tentacle and may, thereby, be lifted up by the growing bulb and become situated on 

 the distal end of the young tentacle; afterwards it gradually loses its rounded form and is finally absorbed. 

 Browne rightly remarks: "If cordyli are the forerunners of tentacles one would naturally expect to 

 see them in the earliest stage or in the very early stages; but they do not make their appearance 



Fi 2 



