RHIZOSTOM.K (' \>S|M1'KA. <t 1.'! 



mouth-arm disk in the full-grown medusa, although they are commonly found near the edges 

 of the disk. The mouths are (ringed with a multitude ot fine, waving tentacles. 



There are 4 small, deep, oval-shaped, interradial subgenital pits, and 4 separate m- 

 vaginated genital sacs. Central stomach is cruciform, being encroached upon at the inter- 

 ladial sides by the 4 sac-like gonads. 1 he axial ducts of the 8 mouth-arms empty into this 

 central stomach at the 4 principal radii. The central stomach also gives rise to twice as many 

 radial vessels in the subumbrella as there are marginal sense-organs. Every alternate vessel 

 extends to a sense-organ, the others going to intermediate parts ot the nm. All of these radial 

 vessels are put into communication one with the other by numerous anastomosing branches; 

 but there is no well-defined circular vessel such as is figured by Haeckel in Cassiopea ornntn. 



There is a well-developed zone ot circular muscle-fibers in the outer halt-radius of the 

 subumbrella. These have a more and more cuspate trend as we near the center ot the disk, 

 there being twice as many cusps as there are radial vessels, the outward convexities of the 

 cusps being between the vessels. 



The general color of the medusa is greenish-gray-blue, the greenish color being due to 

 clusters of commensal plant-cells within the gelatinous substance of the disk near the surface. 

 It the medusa be maintained in darkness for a month this green color disappears, leaving 

 the animal a pale, translucent blue-gray. Around the outer edge of the central concavity 

 of the exumbrella is a wide, dull white circle, edged on its inner side with faint gray-brown. 

 A more or less Y-shaped, radial, white stripe extends outward from the broad ring in the 

 radii of the sense-organs, the sense-organ being in the center of the crotch of the Y. In addition 

 a single, radial stripe extends outward down the middle of the exumbrella side of each marginal 

 lappet. Occasionally these radial stripes are more or less separated from the broad, white 

 circle. Conspicuous spoke-like, white stripes extend outward in the radii of the sense-organs. 

 These are white regions found in the gelatinous substance of the bell and extend half-way through 

 the gelatinous substance from the subumbrella toward the exumbrella surface. The mouths, 

 filaments, and vesicles are olive or olive-brown, the vesicles and filaments being of a decided 

 green. Among the many color varieties there is a rare one in which the spoke-like, dull white 

 spots are diamond-shaped, and there is no broad, white ring on the exumbrella. The whole 

 medusa is more translucent than are the more abundant medusae with the white ring. They 

 are also smaller than the common form. Curiously enough this color variety bears a striking 

 resemblance to Cassiopea ndrosia Agassiz and Mayer, from the Fiji Islands, South Pacific. 

 Various forms of its color patterns are shown in the photographs in plates 70 to 72 taken 

 from lite by the author. 



I find that Cassiopca can thrive well in darkness for more than a month, hence the 

 medusa is not dependent upon its commensal plant cells for the oxygen it requires. In this 

 connection \\hitnev, 1907 (Biol. Bulletin, vol. 13, No. 6, p. 291), finds that if green li\Jra 

 be placed temporarily in a 0.5 to 1.5 per cent solution of glycerin, the green algae (Chlorella 

 vulgaris) pass out through the mouth. Then if the h\Jra be replaced in w : ater it will grow nor- 

 mally, but remains clear and does not regain the green bodies even when placed in an aquar- 

 ium with algx. 



This medusa was discovered in great abundance by Dr. R. P. Bigelow in a salt-water 

 lagoon called the Great Salt Pond, near Port Henderson, Kingston Harbor, Jamaica. It is also 

 exceedingly common in the salt-water moat of Fort Jefferson, Tortugas, Florida, where it is 

 found upon the weedv bottom throughout the summer; and it occurs in many semi-stagnant, 

 salt lagoons along the Florida Reef as far north as Miami. 



The early stages of the development of the egg into the scyphostoma are as yet unob- 

 served, but the process of the formation of asexual buds by the scyphostoma has been elabor- 

 ately studied by Bigelow and observed also by Perkins. The buds arise from the perradial 

 sides of the calyx of the scyphostoma near the point of origin of the stem. Scyphostomae are 

 never found with more than two buds attached. When two are present the older is always 

 attached to the apex of the younger bud. The bud is at first hemispherical, hernia-like; then 

 elongated, and finally spindle-shaped. The ectoderm, entodcrm, and mesogloea of the bud 

 are produced from the corresponding layers of the parent scyphostoma, and the 4 ectodermal, 

 septal muscles of the bud are derived from out-growths of one or both of the septal muscles 

 of the parent which lie in the interradii adjoining the perradial area of hud formation. The 



