RHIZOSTOM.E — COTYUJRHIZA. Hd 1 



Besides these slioit appendages, less numerous but somewhat larger ones terminate in a 

 flattened ball-like to disk-like end set in a socket. At the point of bifurcation of each of the 

 8 main mouth-arms is a filament which is circular in cross-section and nearly half as long as 

 the mouth-arm itselt. This filament tapers gradually from base to tip, but usually terminates 

 in a swollen end. Centripetal to these 8 main filaments are 3 to 5 other, somewhat shorter 

 filaments arising between the frilled mouths of each mouth-arm. Near and at the center of the 

 arm-disk there are numerous slender filaments, about one-third as long as the main filament, 

 which terminate in expanded disk-like conical ends. 



A unitary, cruciform, subgenital space opens outwardly at the 4 subgeiiital ostia. Thus 

 It is possiiile to pass a probe into any one of the subgenital ostia and out through the one 

 on the opposite side ot the arm-disk without penetrating any tissues of the medusa; the 

 subgenital space being actually outer world (C, fig. 410). The complexly folded, genital 

 membrane is developed upon the sides and upper floor of this subgenital space, and thus 

 upon the lower floor of the central stomach. 



The central stomach is large, occupying the spacious cavity of the central dome of the 

 exumbrella (B, fig. 401). 11 to 13 radial-canals per octant (88 to 124 in all) arise from the 

 marg-in ot this central stomach and extend outward to the bell-mariiin. There is no dis- 

 tinct ring-canal, but instead there are numerous, lateral anastomoses between the radiating 

 canals, forming a complex network of vessels under the floor of the subumbrella. The main 

 canals of the 8 mouth-arms empty by 8 adradial openings into the central stomach. Each 

 of these mouth-arm canals bifurcates, and the two main branches give rise to numerous, 

 lateral diverticula which lead to the gutters of the frilled mouths. 



There is a well-developed unitar\', marginal ring of circular muscles and an inner zone 

 of radial-muscles in the subumbrella. Bethe, 1903, has shown that when the medusa pulsates 

 these inner-lying radial-muscles contract before the ring-muscles, though the latter lie nearer 

 to the sense-organs, from which the contraction-impulse arises. This more rapid response 

 of the radial-muscles is due to the fact that their latent interval between the reception of the 

 stimulus and their response is less than in the case of the circular muscles. Bethe also finds 

 that the normal pulsation consists of 80 to too contractions at fairly regular intervals with 

 periods of total rest between them. These are then followed by a pause which lasts as long 

 as 3 to 20 of the normal pulsations. For further details of the character of the pulsation, the 

 reader should refer to Rhizostoma pidmo. 



The bell ot this medusa is rich olive, tending to orange, or to brownish-yellow, being 

 especially dark and brownish on dome-like apex of the exumbrella. The rich yellow color 

 is found on both exumbrella and subumbrella, and is due to the presence of numerous yellow- 

 to brown plant cells (/.oochlorelhr) which float in the canal-s)Stem and intest the entoderm 

 of the medusa. Claus, 1883, finds these cells in the 8 lobed eph\ra when only 1.5 to 2 mm. 

 wide. 



The arm-disk and mouth-arms are usually pale milky-white tinged with delicate creamy- 

 yellow. The free outer edges of the mouths are tinged with purple var\ing to blue or violet. 

 The terminal portions of the appendages, which arise between the trilled mouths, are deep 

 blue tending to purple, or violet. 



This medusa is found in the Mediterranean, but is quite capricious in its appearance, 

 being at times very rare. According to GraefFe it is not seen every year in the Adriatic at 

 Trieste, but adult medusae are usuall}' seen from Jul)' to September, while small ones are tound 

 in July and August. At Naples adult medusae are commoner trom August to October than in 

 winter, when they become very rare, being only occasionally found in mid-winter. Keller is 

 of the opinion that this medusa is a deep-water species which only occasionally comes to the 

 surface when sexually mature, and that the young remain near the bottom ot the sea. Van- 

 hotFen, 1888, records the capture of a young individual of this medusa at Assab in the Red 

 Sea on June 10, 1885. The medusa must have been introduced into the Red Sea through the 

 Suez Canal. It has also been found in the Atlantic, near the Canary Islands. (See C. amhu- 

 lacrata Haeckel.) 



The development of this medusa has been studied bv Busch, Frantzius, Gegenbaur, 

 Kowalevsky, Claus, Goette, du Plessis, Hein, and others, and has furnished some ot the 

 evidence for a controversy between Claus and Goette concerning the development ot the gastro- 

 vascular cavity of the scyphostoma. 



