RHIZOSTOM/E. 633 



the same thing in Casstopea. In Cdssiopcn xaiiinr/ituui R. V. Bigelow showiil that the- rhopaha 

 are derived I'roni every ahernate tentacle of" the scyphostoma, the otiier tentacles degenerating 

 wholly. I find that in this medusa when the rhopalium regenerates it gives rise to a short lateral 

 branch thus tending in an abortive manner to regenerate the tentacle, from which it originally 

 came. 



Many observations have been carried out ui)on the embiyology of" Rhizostomae, and 

 reviews of these researches will be found in the descriptions of Casstopea xamachana, Cotyl- 

 orhiza tubercidata, Rhizostoma pulmo, Mastigias papita, Phyllorhiza punctata, and Stomo- 

 lophus meleagris. Claus, Goette, R. P. Bigelow, Kowalevsky, von Lendenfeld, and Vanhiiffen 

 have been especially active in these researches. 



Haeckel, 1880, considered the presence or absence of a unitary, cruciform, genital cavity 

 to be of great systematic importance and sought to separate families upon this distinction; but 

 Claus, von Lendenfield, Vanhiiffen, Maas, and Browne have demonstrated that this is a matter 

 of no great import, for in different individuals of the same species we may find in some cases 4 

 separate genital sacs, while others ha\e a cruciform genital cavity, and still others may have 

 a more or less complete coalescence and breaking apart of the partitions in some quadrants 

 and not in others. It is therefore evident, as was first clearly shown by Claus, 1883 (Organ- 

 isation und Entwick. Medusen), that the conditions exhibited by the genital sacs afford no 

 criteria for the distinction even of genera, much less of families. Indeed, Haeckel's system 

 leads to the separation of closely related forms and the close approximation of remotely 

 related forms, and is quite artificial. 



Claus, 1883, 1886, and Vanhoffen, 1888, have attempted to separate the families of 

 Rhizostomae upon the distinctions afforded by the manner of branching of their mouth-arms. 

 Claus's system somewhat modified by von Lendenfeld, 1888 (Zeit. fijr wissen. Zool., Bd. 47, 

 p. 208), distinguished nine families as follows: 



Rhizostom.^: Scvphomedusx without marginal tentacles and with 8 adradial mouth-arms. 



ArchirihizidiE: Mouth-arms unbranched. Gastrovascular network simple. No central mouth. 



Cassiopeida'. Arm-disk fiat. Arms long, irregularly branched with appendages. Radial-canals numerous. No central 

 mouth. 



Craunostotnid^F: Arm-disk wide, style-shaped, arms dichotomously forked. Arm-margins free, with clubs. Centripetal 

 canals end blindly. Subgenital porticus unitary. Central mouth-opening present. 



Cepheidtr: Arm-disk wide and flat. Arms dichotomously forked, with 2 of the axial, terminal wings turned outwards. 

 With clubs. No direct central mouth-opening. 



Lychnorhhidir: Arms 3-leaved or distally 3-winged. 8 or 16 radial-canals. Gastrovascular network simple. No central 

 mouth. 



Siomolophidie: Arm-disk style-shaped, elongate, with 8 pairs of lateral "shoulder ruffles" or "scapulets." Proximal 

 parts of the arms fused into a tube, distal parts branched. 16 radial-canals, with well-developed net-work of con- 

 necting vessels. No central mouth. 



Rhizostomide: Arm-disk style-shaped, elongate, with 8 pairs of lateral "scapulets" with clubs. Lower-arm three- 

 winged, with dorsal mouths. 16 radial-canals. Centripetal network of canals well-developed. No central mouth. 



Catostylids: Arm-disk very wide, elongate, and style-shaped. Lower arm 3-winged w'ith dorsal mouths. No centrip- 

 etal networks of canals. Subgenital porticus unitary. No central mouth. 



Leptobrachidir: Arm-disk wide and fused with the upper arms. Lower arms long, ribbon-shaped, and 3-winged. 

 Simple canal net spread over the entire subumbrella. Subgenital porticus unitary. No central mouth. 



A simpler system is proposed by Vanhoffen, 1888 (Bibliotheca Zoologica, Heft 3), who 

 divides the Rhizostonne into 7 families: 



Rhizoaomata simplicia: Mouth-arms simple and unbranched. All of these are apocryphal, having been seen only 



by Haeckel and Fewkes. 

 Dichotoma: Mouth-arms dichotomously forked, with lateral expansions. 

 Pinnata: Elongate mouth-arms pinnately or irregularly branched. 

 Triplera: Mouth-arms 3-winged. Each mouth-arm with a ventral and 2 dorsal lamella? which meet at a point at the 



lower end of the arm. 

 Trigona: Identical with the Rhizoitomata triptera. 

 Lorijera: Mouth-arms elongate, lash-like, and triangular in cross-section; with mouths developed along the 3 angles 



of the arms. 

 Scapulata: Mouth-arms with simitar-shaped "scapulets" or "ruffles" projecting from their dorsal sides. 



As was pointed out by Maas, 1903, Vanhiiffen's Triptera and Trigona are identical 

 and should be united, thus reducing his families to six. Schultze, 1898, showed that the 

 mouth-arms of the "Dichotoma" of Vanhoffen are not forked at their outer ends, but give 

 rise to 2 broad, longitudinal, lateral lamellae, which may branch secondarily. With these 

 modifications Vanhiiffen's system affords the readiest means of classifying the Rhizostomae, 

 being based upon the mutations of the most conspicuous organs, the mouth-arms. 



