MEDUSA. I. 



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

 than the corresponding organs in Chro)iiatoncma rubrum. — In another nearly related species, Cliroviato- 

 nema hertwigi (Ptychogcna hrrtwigi 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 Laodiceidcr, a series of transitional forms of cord>li from cylindrical 

 or spindle-shaped with a distal cluster of nematocysts {Chromatoncma 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 Laodiceido- and the Tiaridcr^ 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 Cliroinatoiicina rubrjini. The species 

 in question is Tiaranna rotunda (Quoy & Gaimard). 



I deeply regret that my paper on the Authomedusa^ and 

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

 been printed, as two species of the interesting genus Tiaranna have Fig. ,. r.-,rt of the l.dl-marKin of Tiaranna 



, 1 ,.•.,•., . r u .^ t r ii rotunda X)uov & Gaimard). 



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



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

 Laodiceido'. As especially Tiaranna rotunda is of great interest in this respect, 1 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 rotunda (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 Cliromatoncma, only they are 

 never c\-liudrical, 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 cord\li of Chromatonona. 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 mcrtensiL 

 Browne has discussed this question in his paper. Revision of the ... Laodiceida {xofi']. 

 p. 458). Browne has examined a large number of specimens of Laodicea undtdata (early 

 and intermediate stages). He is of opinion, that transformation of cordyli into tentacles 

 the°(UstS ^°^^ "°^ *-^^^ 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 

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

 the distal end of the voung 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 



Fig. 2. 

 Dwarf-tent- 

 acle of Tia- 

 ranna rotunda 

 (Quoy & Gai- 

 mard), with 



numerous 

 nematocysts 

 at 



end 



