TYPES OF CELENTERA—AURELIA AURITA. 157 
emphasises the fact that the radial symmetry is first indicated by the 
gut pockets, and the tentacles are late in development. Goette 
describes a quite similar process of development_in certain sea- 
anemones, and claims to have found there rudiments of septal pockets 
and ectodermal muscles, thus confirming his view of the intimate 
relation between the Anthozoa and Scyphomedusz. 
The larva now forms a ‘‘ Hydra-tuba” or ‘‘Scyphistoma”; it is 
about an eighth of an inch in height. By lateral budding, or by the 
formation of creeping stolons, it may givé rise to larve like itself. 
The gradual widening of the central cavity renders the gullet tube 
less obvious, and results in an increasing resemblance to the medusa 
type. 
In late autumn, however, a more fundamental change occurs in the 
history of the Hydra-tuba. (a) Occasionally, as has been observed by 
Haeckel, the Scyphistoma becomes detached and converted into a free- 
swimming Ephyra, which in turn becomes a jelly-fish. (4) Sometimes, 
in unfavourable conditions, 4 furrow appears round the upper region of 
the Scyphistoma, the upper portion is converted into an Ephyra, and 
floats away, while the lower portion re-forms its oral region by regenera- 
tion, and produces another Ephyra. (c) In ordinary conditions the 
Scyphistoma elongates, and displays a succession of annular constric- 
tions. This stage, often compared to a pile of discs or saucers, is 
called a Strobila. Each disc is separated off in its turn as a free- 
swimming Ephyra, which becomes a jelly-fish. The still undivided 
basal portion may rest for a time, and then undergo further con- 
striction. This is probably an abbreviation of the primitive mode of 
development, 
In the conversion of the Scyphistoma into the Ephyre, the diverticula 
coalesce into a general cavity, the entrances to the septal invaginations 
probably persist as the sub-genital pits, the gastric filaments sprout out 
from the remains of the septa, and so mark the place where the ecto- 
dermal gullet passed into the endodermal cavity. : 
The first Ephyra differs from those which come after it in bearing the 
original tentacles of the Hydra-tuba. From its margin eight bifid lobes 
grow out, each embracing the base of a perradial or interradial tentacle. 
The bases of these eight tentacles become the sense organs or rhopalia. 
The other eight adradial tentacles atrophy. On the Ephyre which 
follow there are at first no tentacles, only the eight bifid marginal lobes 
which bear the sense organs in their niches. 
This development illustrates alternation of generations, From the 
fertilised ovum a fixed asexual Scyphistoma results. This grows into a 
Strobila, from which transverse buds or Ephyree are liberated. Each 
of these grows into a sexual jelly-fish, producing ova or spermatozoa. 
Relatives of Aurelia.—The Meduse, or true jelly-fish, include 
forms which agree with the Anthozoa in relative complexity of 
structure as compared with Hydrozoa, and in the possession of 
an ectodermal gullet, but differ in possessing ectodermal septal 
muscles and in some histological features. If Goette’s discovery of 
rudimentary ectodermal muscles in the larve of certain sea-anemones 
be confirmed, however, it would greatly increase the probability of 
a close relationship between the two sets. Among the Scyphomedusz 
