624 



MEDUSAE OF THE WORLD. 



Dimensions in mm. of a mature specimen of Aurellia aurita from Naples, Italy, captured 

 May 30, 1900. Bell-radius, 85; length of mouth-arms, 75; width of genital cross, 51. (See 

 text-figure 397.) 



The following is a description of the American form of Aurellia aurita, which has been 

 commonly called "A. flavtJula": 



Adult medusa. Disk 140 to 250 mm. wide, 50 to 90 mm. high. When expanded it is 

 flatter than a hemisphere, but when contracted it becomes hemispherical. Gelatinous sub- 

 stance tough, thick at center, but thin at edge of disk. 8 marginal sense-organs at the bottom 

 of shallow niches between the 8 broad velar lappets. Each sense-club is blunt and contains 

 an ectodermal, proximal ocellus on the exumbrella side, a cup-like pigmented eye composed 

 of both ectoderm and entoderm on the subumbrella side, and a distal entodermal mass of 

 crystalline concretions. It is partially protected above by a bridge-like web stretching between 

 the adjacent lappets. Lappets of considerable size on both sides of the club. 



A single median pit projects downward from exumbrella surface just above the sense- 

 club. Small and numerous tentacles arise from sides ot disk at a slight distance above margin 

 and alternate with an equal number ot small, elongate, marginal lappets which similarly arise 

 from the sides of the disk above the projecting margin. Tentacles hollow, with longitudinal 

 strands of muscles down their subumbrella sides, and with broken rings of nematocyst-cells 



on their exumhrella sides. Margin ot disk 

 entire and simple except at places of the 8 

 sense-organs, where it is broken by notches. 

 It forms a narrow, velum-like structure 

 lying below the tentacles and marginal lap- 

 pets. Central mouth-opening 4-sided, sur- 

 rounded by 4 thick, stiff, gelatinous mouth- 

 arms, the 8 free edges of which are much 

 convoluted and provided with a row of 

 numerous, small tentacles. These tree 

 edges inclose a median trough or gutter, 

 which extends down the middleof thelower 

 side of each mouth-arm. These mouth- 

 arms are each about as long as the radius 

 of the disk; at their bases they are broad 

 and their free margins are here greatly 

 indented and folded in sinuous lines bor- 

 dered by small tentacles. The 4 interradial 

 gonads are horseshoe-shaped and alternate 

 with the mouth-arms, and their position 

 is marked on the floor of the subumbrella 

 by 4 thick, horseshoe-shaped thickenings 

 of the gelatinous substance, in the center 

 of each of which there is a deeply sunken, subgenital pit. The radius of each of these horse- 

 shoe-like regions is about one-third that of the disk itself. 



Goodey, 1909, finds 4 interrradial, canal-like grooves in the subumbrella floor of the 

 stomach leading from the gonads to the folds of the oral arms and serving to conduct the 

 genital products away from the gonads. 



The central stomach occupies a 4-lobed space, its outline being determined by the periph- 

 eral edges of the 4 horseshoe-like genital cavities, and it gives rise to a complex system of 

 radiating canals extending from edges of stomach to circular canal at bases of marginal ten- 

 tacles. 8 separate, straight, non-anastomosing, adradial canals and 4 radial and 4 inter- 

 radial, pitchfork-shaped systems of anastomosing canals; each of these systems consists of 

 a single, straight, median canal and a pair of branching, lateral canals, which arise on either 

 side of the median canal very near the periphery of the central stomach-cavity. The lateral 

 canals each give rise to 3 to 5 radiating branches which anastomose sparingly and extend 

 outward to the circular canal. These branches decrease in caliber and anastomose more 

 frequently as they approach the circular canal. The gonads are found in 4 horseshoe-shaped 



FIG. 397. Aurellia aurita. Drawn by the author, from a specimen 

 found at Naples, Italy, by Dr. S. Lobianco at the Naples 

 Zoological Station, May 30, 1900. 



