Boone, Coelenterata, Cruises of "Eagle" and "Ara," 1921-28 43 



sense organs. There is also a single radial stripe extending outward 

 down the middle of the exumbrella side of each marginal lappet. 

 Prominent spoke-like white stripes extend outward in the radii of the 

 sense organs. The mouths, filaments and vesicles are olive or olive- 

 brown; the vesicles and filaments more frequently being decidedly- 

 green. A number of color varieties of this species are known. An 

 especially striking form is the rare one with dull white diamond- 

 shaped markings. 



Life history : The early stages of the development of the egg into 

 scyphostoma are not yet studied. The formation of asexual buds by 

 the scyphostoma has been critically studied by Bigelow and also 

 observed by Perkins (1905). A careful resume of this phase of the 

 development of the species has been presented by Mayer (1910). 



Regeneration in this species has been carefully studied by Stockard 

 (1907) and Zeleny (1907). Histology of the muscles has been dis- 

 cussed by Dahlgren and Kepner (1908). 



Studies of the rhythmical pulsation and its causes in the medusa 

 have been reported by Mayer (1906, 1908). 



Technical description: Mayer states that the disk diameter is 

 usually 150 mm. Bigelow has recorded a specimen from Jamaica 

 with a disk diameter of 240 mm. The disk is flat with rounded edges, 

 the exumbrella with a median concavity the diameter of which is about 

 equal to the disk radius, this concavity forming a sucking disk. The 

 number of rhopalia is regularly 16, but often varies from 17 to 23. 

 This variation is determined at the time of stabilization and is not 

 related to the size of the medusa. The sense organs are short, blunt, 

 clavate, and are set within niches protected above by a shelf-like 

 membrane spanning the cleft between adjacent lappets. No exum- 

 brella pit occurs above the club. Each sense organ contains an ecto- 

 dermal ocellus with reddish brown pigment. There are five short, 

 blunt, rounded lappets between each successive pair of sense organs ; 

 the two lappets adjacent to sense organs are only about half as 

 wide as the others of the series. The mouth-arm disk which projects 

 as a flattish plate from the center of the subumbrella is only about 

 two-thirds as wide as the disk radius. Eight oral arms arise from 

 this disk, each being rounded and slender with ten to fifteen alternate 

 primary branches and numerous smaller ones. The arms project some- 

 what beyond the margin of the bell. There is a single flat ribbon-like 

 filament in the axil of each primary branch of the oral arms. There 

 are also five to thirteen ribbon-like filaments on the oral surface of 



