124 



OF THE WORLD. 



This medusa is very variable in color. The stomach ranges from yellow to red, or from 



brownish-red to purple. The radial and circular canals may be colorless, to yellow or green. 



The ocelli are red or dark brownish-purple. The tentacles range from colorless to light-purple. 



It is widely distributed over the North Atlantic and in the Mediterranean, but it 



appears to be much commoner on the European than along the American coast. 



The development has been studied by Hamann, 1883, and Metschnikoff, 1886. Seg- 

 mentation is total and equal and a single-layered, elongate, ciliated larva is found. The 

 entoderm develops from cells which wander into the central segmentation cavity from the 

 hinder end of the larva, so that finally a two-layered planula is formed. The planula attaches 

 itself and the hinder end develops into a hydrorhiza, while the forward end becomes the 

 polypite. The hydrorhiza becomes invested with a thin pensarc and the polypite develops 



a mouth and 2 or 3 long thin tentacles, which arise at the base 

 of the conical throat-tube. This stage was reached at the 

 end of 16 days in Metschnikoft's specimens, and apparently 

 the hydroid is one ot the Clavidae. 



This hydroid may possibly be the very abundant and 

 widely distributed Pengonimits rrpens (fig. 66) found oft the 

 Atlantic coasts of Europe from Russia southward, in the 

 Mediterranean, off the Pacific coast of the United States, 

 and at the Falkland Islands and Terra del Fuego, South 



o 



America. 



The stems of the hydroid branch and are covered with 

 a gelatinous investment to which foreign bodies become 

 attached. The polypites are spindle-shaped, with a single 

 oral circlet of tentacles. The medusa-buds arise singly from 

 the sides of the stems. 



According- to Hartlaub and Browne the medusa is set 



P> 



free with but 2 tentacles and 2 small tentacle-bulbs. Forbes 

 described the 4-tentacle stage as Oceania titrnta. the 8-ten- 



o 



tacle condition as O. octona, and the medusa with 12 tentacles 



as 0. episcopalu. 



Some of the recent literature relating to the hydroid P. 

 repens is here presented, though it must be borne in mind that this has not been proven to 

 be the hydroid of the medusa in question. 



Pengonimits re pens + P. minutus, ALLMAN, 1872, Monog. Tubul. Hydroids, p. 521, plate II. 



Perigommus repens, GRAEFFE, 1884, Arbeit. Zool. Inst. Wien., Bd. 5, p. 350. (At Trieste, Adri- 

 atic. Rare. Medusae produced in May). DU PLESSIS, 1888, Recueil Zool. Suisse, tome 4, 

 p. 539. BROWNE, 1896, Proc. Zool. Soc. London, p. 462 (P. minutus ALLMAN = P. repens). 

 BONNEVIE, 1899, The Norwegian North Atlantic Expedition, 1876-1878, vol. 26, Hydroids, 

 p. 41 (from Norway). CALKINS, 1899, Proc. Boston Soc. Nat. Hist., vol. 28, p. 539, plate 

 I, figs. 3-3 D (from Puget Sound). TORREY, 1902, California Univ. Pub. Zool., vol. I, 

 p. 29 (Pacific coast, California to Washington). HARTLAUB, 1905, Zoolog. Jahrbiichern, 

 Suppl. 6, p. 530, fign. K, L, M (from the Falkland Islands and Terra del Fuego). 



Turris rotunda. 



l>i,in,ra rotunda, QUOY ct GAIMARD, 1827, Annal. des Sci. Nat., tome 10, p. 181, plate 6 A, figs, i, z. 



Tiara rotunda, HAECKEL, 1879, Syst. der Medusen, p. 57, taf. 3, fign. 9, lo. BEDOT, 1905, Revue Suisse de Zool., tome I}, 

 p. 151 (all literature to 1850). 



Bell cubical without a pointed apex; 20 mm. high, 20 mm. wide. Bell-cavity only two- 

 thirds as deep as the bell-height. 8 tentacles much longer than the bell-height, with conical 

 basal bulbs. A large, dark-red ocellus on the outer side of each tentacle-bulb. Stomach 

 small, swollen, globular, and confined to the upper third of the bell-cavity. The lips are short, 

 much folded, and with a row of nettling warts around their edges. The gonads consist of 

 4 pairs ot longitudinal, swollen areas, each thrown into 8 to 10 cross-foldings, on the adradial 

 sides ot the stomach. The stomach, gonads, and tentacle-bulbs are carmine, lips rose-red. 



1 i'.. i<>>. Perigonimus repent, after Him k 

 in British Hydroid Zoophytes. 



