MEDUSAE. 15 



and dendritic in shape, forming a kind of ornamental border to the radial and circular 

 canals. Haeckel calls these diverticula " leberartigen Canal-Dcusen," but there is no 

 evidence that they function as glands. The diverticula of the radial canals in the 

 early stage of Catablema wddoni are simply short lateral outgrowths without any 

 1 (ranching. In the adult, though some of the diverticula are short and simple, most 

 of them are more or less branched. The mode of branching is, however, very variable, 

 and scarcely two diverticula are alike. It is important to notice that the diverticula 

 are long and that some nearly meet those from the adjacent radial canals ; there is 

 no definite arrangement of the diverticula upon the sides of the canals. They are 

 sometimes in opposite pairs, sometimes alternate, and apparently develop wherever 

 there is a sufficient space. In some of the other species of Catablema the circular 

 canal has diverticula upon its upper margin, similar to those upon the radial canajg. 

 In Catablema weldoni the diverticula of the circular canal have disappeared, and their 

 former presence is just indicated by a few minute vestigial outgrowths. 



The most interesting feature of this Medusa is the presence of filaments (Plate I., 

 fig. 4) along the inner side of all the tentacles. The filaments are closely packed 

 together, forming a kind of frill which extends along nearly the whole length of the 

 tentacle, being absent from the basal portion only. The crowding together of the 

 filaments, so as to form thick dense masses, depends entirely upon the contraction 

 of the tentacle. In a semi-contracted tentacle the filaments are about four deep, 

 transversely, and when the tentacle is closely contracted they are denser still. In a 

 fully-expanded tentacle the filaments are probably arranged in a single or double row, 

 and then they should somewhat resemble the appearance of the filaments on the 

 tentacle of Ctenaria ctenophom. In some of the specimens, owing to great shrinkage, 

 the tentacles have the appearance of long narrow ribbons, with one edge lined with 

 filaments. 



The state of preservation of the specimens is not good for minute histological 

 details, but is sufficiently so to show that the filaments are composed of ectoderm cells. 

 The filaments are solid, and have a central strand of mesoglaea. They are capable 

 of a certain amount of expansion and contraction. There is no visible evidence that 

 the endoderm of the tentacle enters the filament. Sections through the tip of a 

 filament show that it coutains numerous very minute nematocysts. 



The tentacles are frequently very long ; some measure 60 to 80 mm. in length, 

 and are by no means fully expanded. They are hollow and well supplied with 

 ectodermal muscle fibres. 



The basal bulbs of the tentacles are laterally compressed and curve over the thick 

 margin of the umbrella. There is not the slightest indication of a pigment spot on 

 the basal bulbs, nor of any other kind of sense organ. Between every two tentacles 

 tlie.rc is a small marginal bulb, which is probably capable of developing a tentacle 

 when another is needed. 



One specimen has nine long tentacles, with a small bulb in between every two 



