62 MEDUS.'E OF THE WORLD. 



In 1848 Forbes described this medusa from Penzance Bay, southern England, where 

 it was abundant in August, 1846, and in 1879, and where I found it in November, 1907. 

 Haeckel describes that which may prove to be the same species from the Mediterranean. The 

 points of difference between the two medusae will be brought out in the following description. 



The bell is bell-shaped; in Forbes's medusa (fig. 23) 3 mm. wide and 4 high; in Haeckel's, 

 (fig. 24), 8 mm. wide and 8 mm. high. Forbes's medusa lacks an apical projection, while 

 Haeckel's has a short, conical, pointed apex. Also, in Forbes's medusa there was no axial 

 canal above the stomach while in Haeckel's there was a narrow, axial vessel. Moreover, 

 in Haeckel's medusa the margin of the bell flares outward, while in Forbes's specimen this is 

 not the case. 



It is well known to students of the Anthomedusae that apical projections and axial canals 

 are exceedingly variable, and may be absent or present in individuals of the same species. 

 The outward flaring of the bell may be brought about through contraction. Haeckel's medusa 

 appears to be merely a large, highly-colored specimen of S. prohfera Forbes. 



The 4 marginal tentacles are I to 3 times as long as the bell-height. Their basal bulbs 

 are large and tapering and about as wide as they are long. The tentacles taper gradually 

 from base to shaft and are hollow. Clusters of I to 3 medusa-buds at a time are developed 

 upon the tentacle-bulbs immediately below the bell-margin. When set free these medusas 

 are already producing another asexual generation of medusas upon their tentacle-bulbs. 

 The 4 radial-canals and ring-canal are straight and very narrow. The manubnum is spindle- 

 shaped and nearly as long as the bell-height in Haeckel's, but not half so long in Forbes's 

 medusa. The mouth is at the end of a narrow neck and is a simple, round opening. The 

 stomach is encircled by the gonad, leaving the base and the throat-tube free. 



Entoderm of tentacles and manubnum yellow to orange or sage-green. Each tentacle- 

 bulb bears a prominent ectodermal brown-colored ocellus. 



If it be true that Forbes's and Haeckel's forms are identical the medusa must range from 

 southern England to the Mediterranean. It appears to be rare and its hydroid is unknown. 



Allman, 1871 (p. 83, fig. 38). gives a figure of a medusa which closely resembles Forbes's 

 Sarsta prohjera. 



I found numerous specimens of this medusa off Mousehole, Mounts Bay, Cornwall, 

 England, early in November, 1907. They accord well with the descriptions of Forbes 

 and of Busch. The entoderm of the manubrium and tentacle-bulbs was sage-green; the 

 tips of the tentacles light reddish-brown, and occasionally there was some reddish-brown 

 pigment in the central entoderm of the stomach. The gonad encircled the stomach, leaving both 

 ends of the manubrium free. 



Sarsia gemmifera Forbes. 



Sarsia gemmifera, FORBES, 1848, British Naked-eyed Medusae, p. 57, plate 7, fig. 2. CHUN, 1895, Bibliotheca Zoologica, Heft 

 19, pp. 4, 7, taf. I, figs. 5, 6 (law of development of medusa-buds). BROWNE, 1905, Proc. Roy. Soc. Edinburgh, vol. 25, 

 p. 757. BROCH, 1905, Bergens Museums Aarbog, No. 1 1, p. 4. 



Codonium gemrniferum+ Sarsia sipfionophora, HAECKEL, 1879, Syst. der Metlusen, pp. 15, 20, taf. I, fig. 4. 



Codonium gcmmifcrum, BEDOT, 1905, Revue Suisse de Zool., tome 13, p. 132 (citation of literature to 1850). 



Purena gemrtiifera, HARTLAUB, 1907, Nordisches Plankton, Nr. 12, p. 58, figs. 54-58. 



This medusa is tound off the Atlantic coasts ot Europe from Norway southward. 

 Haeckel's Sarsia "siphonopliora" from the Canary Islands is probably another name for the 

 same species. 



When young the medusa produces medusa-buds upon its manubrium. These arise in 

 a spiral line, one following the other, down the sides of the manubrium. The oldest of the 

 primary medusa-buds is nearest the base (uppermost) and the youngest nearest the mouth 

 of the manubrium. 



These primary medusa-buds are attached to the sides of the manubnum by short pedicels, 

 and secondary and tertiary medusa-buds arise from the sides of these pedicels. Thus when 

 the oldest (uppermost) original medusa-bud is set free, the secondary bud upon its pedicel 

 remains attached to the manubrium and continues to develop, and when it in turn is set free 

 the tertiary bud completes its development; this process takes place with each and every 

 one of the series of buds. 



