MEDUSA. I. 



Eutima el'ephas (Haeckel) ^quorea forskalea Peron & Lesueur 



Octorchis gegenbauri (Haeckel) Zygodactyla groenlandica (Peron & Lesueur) 



Eirene viridula (Peron & Lesueur) 



Family Laodiceidae Browne. 



"Leptoniedusse with cordyli, commonly called sensory clubs, on the margin of the umbrella" 

 (Browne 1907, p. 459). 



Browne has, no doubt correctly, ascribed the significance as a family-character to the peculiar 

 organs called cordyli. Before I enter into a further discussion of these interesting organs, I will, for 

 the sake of comparison, shortly call attention to the structHre of another kind of marginal appendages, 

 occurring in several Leptomedusse: viz. the Cirri. A cirrus is lengthened, thread-shaped, and is always 

 inserted directly on the margin of the umbrella without possessing a basal bulb. The entoderm of the 

 cirrus is in connection with the entoderm of the circular vessel, and it is solid (not hollow), consisting 

 of a single series of cylindrical or disk-shaped entoderm-cells. The ectodermal epithelial cover is very 

 delicate, consisting of flattened polygonal cells. The cirri carry nematocysts, usually in considerable 

 number, and particularly towards the distal end. The distal part of the cirrus may, as a rule, be spi- 

 rally curled up. 



A typical, fully developed Cord yl us is club-shaped with a thin stalk and a swollen distal 

 part; it may or may not be mounted upon a small tubercle on the bell margin. In opposition to the 

 cirrus, it possesses a hollow central space which, however, may be more or less obliterated; particularly 

 the lumen has often entirely disappeared in the narrow part, the lumen of the distal thick part 

 thus being separated from that of the circular vessel. The entoderm consists of a single layer of large, 

 usually cubical cells surrounding the central lumen. The ectoderm is fairly thin, but not so thin as 

 the ectoderm of a cirrus. There are no nematocysts. This is the shape of a typical cordylus. A very 

 interesting kind of cordylus, not so highly developed, has been observed by Browne in Ptychogena 

 aiifarctica Browne (Browne 1910). The cordyli of that species, as figured by Browne (Plate 2, figs. 7 — 9) do 

 not possess the well-marked club-shaped appearance as in the case of the typical cord\li, but are only slightly 

 more thickened distally than proximally; moreover, in some of them nematocysts were found. 



I am of opinion, that the small marginal appendages in Cliro»iatoncnia ntbriit/i indicate a 

 still lower stage of development of cordyli (see Plate L figs. 2 and 3). They differ from typical 

 cordyli by the possession of a cluster of nematocysts in the distal end and by the general shape which 

 is cylindrical or spindle-shaped. But the ground plane, the structure of the cell-layers, is exactly as in 

 a cordylus. Through the cordyli of Ptychogena antarcHca, mentioned above, as the transitional form 

 they may, I think, without difficulty be homologized with real cordyli. They may not be called cirri, 

 as they have a central lumen, and because they are short and rigid. In a nearly related .species, 

 Chromatonema crythrogonon {Ptychogena erythrogonon Bigelow), further mentioned below, Bigelow 

 found a few cylindrical "cirri" with nematocysts and, besides, a number of spindle-shaped "cordjli" 

 without nematocysts. Excepting the lacking of nematocysts, these cordyli have exactly the same shape 

 as those of Cliromatoncma rtibritm, and they occupy a corresponding position on the bell margin. 



