586 



MEDUSAE OF THE WORLD. 



tiary tentacles; in fact, the tertiary tentacles do not usually make their appearance until 

 the medusa is about 130 mm. in diameter and the lappets remain undivided until the medusa 

 is mature, although Hargitt shows that this is subject to great individual variability. Thus 

 in immature medusae of large size there are usually but 24 tentacles and 32 marginal lappets, 

 and the animal is in the "Chrysaora stage." I believe, also, that they often mature in this 

 stage and never reach the Dactylornetra condition. 



The primary and secondary tentacles are very long and flexible while the tertiary ten- 

 tacles are only a few millimeters in length. In like manner the lappet-clefts of the primary 

 and secondary tentacles are deep and the lappets almost as long as they are broad; while 

 the lappet clefts of the tertiary tentacles are mere shallow notches in the contour of the lappets 

 adjacent to the sense-organs. Mouth-opening cruciform, in center of subumbrella, at extremity 

 of a 4-cornered oesophagus and surrounded by 4 mouth-arms or palps, which when fully 

 extended are about 3 or 4 times as long as the bell-diameter. The 8 free edges of the mouth- 

 arms are complexly crinkled and highly flexible. The central stomach occupies a wide lentic- 

 ular space in the midst of the bell and gives rise to 16 simple, radiating pockets, 8 in the 

 tentacular and 8 in the rhopalar radii. These pockets are completely separated one from 

 another by 16 radiating septa which join the upper and lower walls of the umbrella cavity 



together. The tentacles are hollow 

 throughout the greater part of their 

 length and their entoderm is ciliated 

 as is that of the stomach itself. 



The gonads are contained in 4 

 interradially situated, entodermal in- 

 foldings of the wall of the subum- 

 brella, and their position is marked 

 by 4 deeply sunken, subgenital pits. 

 The genital organs are provided 

 with numerous, simple, unbranched 

 gastric cirri which project inward 

 into the stomach-cavity. There are 

 two sets of radial muscle-fibers; the 

 principal set is found in the 16 septa 

 between the gastric pouches, and 

 alternating with these in position are 

 16 strands in the exumbrella, 8 of 

 which lead outward to the sense- 

 organs and 8 to the primary tentacles. 

 Color quite variable. In some 

 individuals the disk is pink, in others 

 yellow with a bluish opalescence. The exumbrella is thickly sprinkled with yellow-ocher 

 colored nettling-warts and there are 16 radiating stripes of reddish color upon the exumbrella in 

 the radii of the septa of the peripheral stomach. These reddish stripes extend about half-way 

 from the bell-margin toward the center of the exumbrella and are due to highly refractive, 

 rosin-colored pigment granules within the epithelial cells of the disk. The male gonads are 

 generally pink, while the ovaries are yellowish or ashy-gray. The radial muscle-strands of 

 the subumbrella are of a glistening white and the entodermal cores of the tentacles are pink. 

 The mouth-arms are pink or yellow and always sprinkled over with red-colored pigment spots. 

 The marginal sense-organs contain each a mass of glistening white concretions, but no ocelli. 

 This species extends from the southern coast of New England to the tropics. In August 

 it is abundant in Tampa Bay, Florida. It has been taken by Bickmore at the Bermudas, 

 and by Drayton between the Bermudas and the Azores. "A well-marked southern variety" 

 was found by Brooks at Beaufort, North Carolina, and is figured in plate 64A. It makes its 

 appearance upon the surface along the coast of New England in August when large medusae 

 are found. The young rarely come to view, but remain in deep water. 



Varieties and development. The egg develops into a free-swimming planula which 

 soon attaches itself to the bottom and develops into a scyphostoma having normally 4 ten- 



FIG, 371. Dactylometra quinquecirrha, after Agassiz and Mayer, in 

 Bull. Mus. of Comparative Zoology at Harvard College. 



