MKDIS.l-:. 29 



visible signs ot" ^loUusa-buds iu auy of the spccimeus, and, it" this species dues 

 reproduce asexually, then some buds should be present in the young stages. It is quite 

 probable that only Eleutheria dichntoma in this genus has Medusa-buds. 



The number of the tentacles increases witii age, and they arc clo.sely packed 

 together round the margin of the umbrella. It is very likely that tlie number of 

 tentacles present when the JMedu.sa is liberated from its Ilydroid corresponds to the 

 number of radial canals, one tentacle being opposite each eaiial. The tentacles opposite 

 the radial canals in the later stages have their ocelli further iu from the margin 

 (Plate III., fig. 2), indiciiting that they are the oldest of the series. Each tentacle is 

 bifurt-itcd or branched, and the bifurcation is visible soon after the first appearance of 

 the tentacle. The upper branch comes ott' close to the uml)rella, and, when fully 

 developed, is provided with ten to twelve clusters of nematocysts arranged laterally 

 in paii-s, and a terminal cluster of nematocysts is also present. When the ])ran(h is 

 expanded (Plate III., fig. l) the clusters are far apart and form an alternating series, 

 liut in a contracted l)ranch (fig. 4) their arrangement is pinnate. It is by the 

 position of these clusters of nematocysts that this species can be easily distinguished 

 from Eleutheria vallentini, which has two or three clusters on the upper (altoral) side, 

 and occasionally one on the under side. The lower branch of the bifurcation is 

 without clusters of uematocy.sts, and it terminates in a slight enlargement, the 

 adhesive disc or sucker, which is composed of specialised ectoderm cells. The 

 tentacles are hollow and the endodermally lined lumen extends along both the 

 branche.s. The basal portion of each tentacle is covered on its under side with an 

 extra thick layer of ectoderm containing nematocysts (Plate III., fig. 3), but there 

 is no enlargement of the nature of a basal bull). B(jtli Eleutlieria dichotoma and 

 /:,'. V(dleiitlni have a continuous band of nematoc^ysts round the margin of the 

 umbrella. This band is absent from E. hodfjsoni, but it is represented by isolated 

 patches of nematocysts on the basal portion of tlie tentacles. 



LEPTOMEDUS^E. 

 Family LAODICIDJi:. 

 Ptvcho(;ena, A. Agassiz, 18G5. 

 Generic Cluiracter. — Laodicidse with four radial canals ; with a central stomach 

 and mouth ; with the ba.sal bulbs of the tentacles without ocelli (Browne, 1907). 



PtYCHOGENA ANTARCTICA. 

 (Plate II., fig.s. G-9). 

 Plychogena antarrlica, Browne, 1007, p. 474. 



In my preliminary notes on the ' Southern Cro.ss ' Hydrozoa I alluded to this 

 Medu.sa under the name of FModice. Later on, when I revised the Laodicidaj, it 

 was placed in the genus Ph/chogenti, and a brief ilescription of the .species was given. 



z 2 



