RHIZOSTOM^ — MASTIGIAS. 



679 



the mouths on the outer sides of the mouth-aims. The central canal of each mouth-arm {^ives 

 oft" 3 side branches which lead to the 3 rows of frilled mouths of the winged, lower parr of the 

 arm. All 3 ot these caTials fuse again with the axial-canal at the base of the ternunal club and 

 extend onward as the axial-canal of the club. 



The central stomach is cruciform and gives off 8 straight radial-canals which extend to 

 the sense-organs. These canals are all connected by a wide ring-canal in a zone at a consider- 

 able distance inward from the margin. About 7 to 9 anastomosing radial-canals arise from 

 the stomach in each octant between the rhopalar canals and fuse with the ring-canal. On its 

 outer side the nng-canal gives off a fine-meshed network, of anastomosing vessels which extend 

 into the lappets and fuse with the outer ends of the 8 rhopalar canals. The circular muscles 

 of the marginal zone ot the subumbrella are widely interrupted in the 8 principal (rhopalar) 

 radii. The gonads are 4 folded walls forming cruciform sides of the subgenilal porticus. 



Color quite variable. Bell and mouth-arms usually greenish-blue, or olive-green to 

 olive-brown, and there are a number of yellow, white, or occasionally brown, blue, or green 

 oval spots over the exumbrella, especially near the margin. The frills of the mouths may be 

 olive, greenish-blue, yellowish-green, or brown. The 8 rhopalar radial-canals are darker. 

 This medusa is widely distributed over the Malay Archipelago, Indian Ocean, and 

 China Sea to Japan, and outward over the Pacific to the Fiji Islands. 



Agassiz and Mayer found an ephyra of the medusa in Suva Harbor, Fiji Islands, in Jan- 

 uary, 1898. It was 5 mm. in diameter and c|uite fiat and disk-shaped. There were 8 marginal 

 sense-organs. The central mass of dark-brown entodermal pigment granules of the sense-organ 

 was developed, but the peripheral shell of transparent granules had not yet made its appear- 

 ance. There were 24 marginal lappets, the 16 ocular lappets being about twice as long as the 8 

 velar lappets. There were 16 radial-pouches from the stomach, of which 8 went to the sense- 

 organs and 8 to the velar lappets. The sub- 

 genital porticus was already unitary and the 

 brachial disk was suspended from the floor ot 

 the subumbrella by means of 4 gelatinous pillars, 

 exactly as in the adult. The ephyra possessed 

 only a simple, central mouth opening, having 4 

 cruciform lips. The margins ot the lips were 

 lined with a row of short, slender tentacles 

 with knob-like ends exactly like those that sur- 

 round the mouths on the mouth-arms of the 

 adult medusa. No trace of the genital organs 

 could be detected, but the gastric cirri were 

 represented by 12 short filaments (3 in each 

 quadrant). The color of the ephyra was very similar to that of the adult. The ring-canal had 

 not yet begun to develop. 



Mastigias papua swims very rapidly by an incessant contraction and expansion of the 

 bell-rim. Being an abundant and variable form, it has given rise to many nearly related 

 varieties, such as M. papua var. sibogcr of the Malay Archipelago and M. siderea ot the east 

 coast of Africa. M. physophora Kishinouye is another variety found abundantly off the 

 coasts of Shima and Sagami, Japan, during summer and autumn. Its bell is at least 100 mm. 

 in diameter and is light-brown with numerous, round, dark-brown spots near the margin. 



Schultze finds this medusa at Amboina, Moluccas, in January and February, and it is 

 evidently only a large, dark-colored variety of M. papua. Kishinouye gives an excellent 

 series of drawings of this medusa. 



Mastigias papua var. siderea. 



Masli^ias siderea, Chu.n, 1896, Jahrb. Wissen. Anstalten Hamburg, Jahrg. 13, p. 13, taf. I, fig. 3. 



Mastigias, sp., (young medusa ?), Schultze, 1898, Abhandl. ScncUenberg, Gesell., Bd. 24, Heft. 2, p. 161, taf. 15, fig. 2. 



Mastyglas siderea, Vanhoffen, 1902, Wissen. Ergeb. deutscb. Tiefsee Exped., Dampfer Valdivia, Bd. 3, Lfg. 1, p. 49. 



(■) Mastigias siderea, Schultze, L. S., 1898, Abhandl. Senckenberg. Gesell. Naturf., Bd. 24, p. 161, taf. 15, fig. 2. 



( ?) Eucrambessa mullerl, Haeckel, 1880, Syst. der Medusen, p. 624. 



{'<) Mastyglas miiUeri, Vanhoffen, 1902, Wissen. Ergeb. Valdlvia Eipcd., Bd. 3, Lfg. I., p. 49. 



Bell flatly rounded, 70 mm. wide. 8 marginal sense-organs and 80 marginal lappets. 

 Ocular lappets narrow, but the 8 intermediate lappets in each octant are semicircular in outline. 



Y\i;. 415. — Mastigias papua, after Vanhoffen, 

 in Valdlvia Expedition. 



