MEDUSiE. 53 



the tentacular series, regularly alternating with the former. Tiic tcnta<:ular canals are 

 evidently not of the same age as the rlmpaliar canals, luit of a slightly later "rowth. 



The tentacles are just Ijeginuiug to make their appearance, and are indicated 

 either Ity bulb-like buds, by tapering elongated buds, or by minute tentacles. Four 

 tentacular buds varying in size and age are found in the smallest .specimens, and as 

 the Medu.sa gi-ows twelve more buds develop, making the total up to sixteen. It is 

 clear that the tentacles d(» not all develop at the .same time, but at irregular intervals 

 and apparently in no definite order. Ultimately the full number is reached, and 

 corresponds to the number of .sen.sc organs. 



It is quite probable that there is a still younger ephyra stage, which is not 

 represented in the collection — a stage with only .sixteen rhopaliar canals, and without 

 the tentacular canals. 



The stomach is very small, circular in outline, and four gastric filaments are 

 visible inside. The filaments increa,se in number as the Medusa grows. In the early 

 stages one filament in each group is much longer than the others, and this is 

 probably the primary one. Tlie mouth is simply a large opening, without any definite 

 lips or arms, which appear later. 



The ex-umbrella is covered with small clusters of nematocysts. In the later, 

 stages the nematocysts are confined to the aboral side of the marginal lobes. 



The circular canal is formed by outgrowths from the radial canals (Plate VI., 

 fig. 2), and is evidently formed just before the branches of the rhopaliar canals bewin 

 to develop. 



The Meta-ephyra stage. — The normal appearance of this stage has been very 

 well figured by Maas (1908, Plate II., fig. 2). It may be distinguished by all the 

 rhopaliar canals possessing two opposite lateral branches, which lead into the circular 

 canal. The tentacular canals remain unbranclied, as in the earlier stiv^e.s. The 

 branching of the rhopaliar canals in the ' Discovery ' specimens is rather irregular, and 

 there is a want of uniformity in the pattern. The number of tentacles or tentacular 

 buds present is very variable and is not correlated with the size of the umbrella, which 

 at this stage is 15 to 25 mm. in diameter. 



Variation. — Among the ephyra and meta-ephyra stages fourteen specimens are 

 sufficiently perfect for counting the number of rhopalia or rhopaliar canals. One 

 specimen has eleven rhopalia, four have fourteen rhopalia, two have fifteen rhopalia 

 and seven have the normal number of sixteen. 



The early stages were mostly taken by the ' Discovery ' during April and May. 

 As meta-ephyra stages were taken at the end of March and ephyra stages in Iklay and 

 June, there is no clue given as to the breeding season of this Medu.sa. The ephyra and 

 meta-ephyra stages were found by the ' Gau.ss ' in Jaimary and March. Vanhoften's 

 account of these stages is based upon nine specimens, 4 to 22 mm. in diameter. 



The Adult. — The adult specimens were all placed in one jar and labelled " Winter 

 Quarters, various dates, 1903. Chromic-formalin." They were afterwards transferred 



2 c 2 



