16 MEDUS.E OF THE WORLD. 



SOLMISSUS, Haeckel, 1879. 



Similar to Cunina, but without otoporpae. 



CvNlSSA = Cnnissa + ^EginoJorus, Haeckel, 1879. 



Nine or more tentacles, and the same number of peronial strands. Peripheral stomach- 

 lobes twice as numerous as the tentacles, being cleft in the tentacular radii. 



jEciNODiscus, Haeckel, 1879. 



Eight tentacles, sixteen peronial strands. Sixteen cleft ( = thirty-two peripheral) stomach- 

 pouches. 



MEDUS/E MILLEPORIN^;. 



Under this heading we may place the degenerate, free-swimming medusae of 

 Millepora. They have no velum and are thus separated from the veiled medusae 

 or Craspedotae. Not only is the velum absent, but the medusa is also devoid of a 

 peripheral canal system and of marginal tentacles. 



The medusae Milleponna? and Craspedotae are doubtless derived from a 

 common ancestral phylum, but have departed widely, one from the other, so that 

 the Craspedotae are constantly characterized by a diaphragm-like membrane, or 

 velum, which partially closes the opening of the bell-cavity at the tentacular margin; 

 whereas this structure is absent in the Milleporinae. 



The only known forms of Medusae Milleporinae are those of Millepora. 



Millepora alcicornis (Medusa). 



Millepora (medusa*), HICKSON, 1900, Proc. Roy. Soc. London, vol. 66, p. 3, figs. i-io. DUERDEN, 1899, Journal of the Institute 

 of Jamaica, March, 1899. HICKSON, 1906, Cambridge Natural History, vol. I, Coelenterata, p. 259, fig. 129. 



Each medusa lies in an ampulla, or cavity, of the corallum, and is attached by a narrow 

 stalk to the innermost part of the wall of the cavity. The bell is 0.4 to 0.6 mm. in diameter 

 and is devoid of radial or circular canals or velum. It consists of a median lamella of entoderm 

 covered on the exumbrella and subumbrella sides by an ectodermal epithelium. There are 

 no tentacles, but instead there are 4 or 5 swollen masses of nematocysts 90 or 72 apart, near 

 the bell-margin, but projecting from the sides of the exumbrella. The manubrium is greatly 

 swollen, and fills the greater part of the bell-cavity. A mouth may (or may not ?) be present. 

 There are I to 5, usually 3 or 4, large ova in the ectoderm ( ?) of the manubrium. The central 

 entodermal cavity of the manubrium consists of an axial chamber which often gives rise to 4 

 perradial pouches which project into the entoderm of the manubrium, and end blindly. In 

 some medusae these pouches do not exist, in other specimens there are but 2 or 3, but probably 

 the most common condition is that of 4 pouches 90 apart. The fully-developed ova occupy 

 positions alternating with the pouches. Dr. Duerden observed that these medusae are set 

 free and swim slowly about with infrequent feeble pulsations. Soon after liberation the ova 

 begin to be discharged into the water and the medusa dies after 5 or 6 hours of life, having 

 discharged all of its eggs. 



The Pacific millepores also produce medusae (see Hickson, S. J., 1891, Quart. Journ. 

 Micros. Sci., 1898; Proc. Zool. Soc. London; and Philosoph. Trans. Roy. Soc. London, B, 

 vol. 179). 



