MEDUSiE. I. 



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

 than the corresponding organs in Chromatoncma rubrum. — In another nearly related species, Chromato- 

 nema hertwigi [Ptychogcna herhvigi 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 Laodiceidce^ a series of transitional forms of cordyli from cylindrical 

 or spindle-shaped with a distal cluster of nematocysts {Chrouinfonoiia riibnivi) through spindle-shaped 

 or slightly club-shaped with or without nematocysts, to the full}' developed form: actually club-shaped 

 without nematocysts. 



As different points of connection exist between the Laodiceido' and the Tinrid(r^ 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 Tiarid(B 

 possesses certain organs, which bear a considerable likeness to the 

 lowest form of cordyli, those of Chroinatonema riibruiii. The species 

 in question is Tiaranna rotunda (Quoy & Gaimard). 



I deeply regret that my paper on the Anthomedusse and 

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

 been printed, as two species of the interesting genus Tiar(7?i}ia have pig. i. Part of tlie beii-margin of T„„an>,a 



1 1 1. -.1 • ,1 . r ^ xi , 1- .1 lotutida lOuoy & Gaimard). 



been dealt with ni that paper; a reference to the accounts of these 



species would have facilitated the following discussion on the relation between the- Tiaridie and the 

 Laodiceida. As especiall)- Tiannuia 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 Tiaraiiim rotunda (textfig. i) are very much like those 

 of Cbromatonema rubrutn. Between every successive pair of tentacles in Tiaranna rotujida 

 there are one or two minute appendages like the cordyli of Chromatoncma^ 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 Chroniatonema. Dwarf-tentacles of a similar shape, though more length- 

 ened, are found in Byttiotiara. 



Hartlaub (1S97) considered cordyli to be juvenile stages of tentacles, and he meant 



to have observed the development of cordyli into tentacles in Staiiropliora mcrtensii. 



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



''&"Gai- P- 45^)- Browne has examined a large number of specimens of Laodicea undulata (early 



Fig. 2. 

 Dwarf-tent- 

 acle of Tia- 

 ranna rotunda 



(Quoy 

 niard 

 numerous 



mardi, wit i ^^^^ intermediate stages). He is of opinion, that transformation of cordyli into tentacles 



neniatocy.sts jQgg j^q(- take place 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 



wav 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 earh- stages; but they do not make their appearance 



