ST ae 

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Order I. 
Acalepha. 
The Jelly-fish are the typical Medus@, and are | water contained in their jelly-like substance. When 
umbrella-like in form, the margin being usually set 
with threads. 
From the middle hangs a stalk which 
Development of Medusa aurita. 
a) First Stage. Freely 
swimming — larva. 
(Planula-Stage.) 
b)Second Stage, Fix- 
ed Polyp (/hdra 
tuba-Stage.) 
ce) &d)Third & Fourth 
Stages. The polyp 
develops tentacles 
and circular con- 
strictions. (Seyphz- 
stoma-Stage.) 
e) Fifth Stage (S¢ro- 
bila-Stage), The 
tentacles disap- 
pear and the con- 
strictions throw off 
young freely swim- 
ming Meduse. 
surrounds the mouth. They are rather large animals) 
and exhibit a beautiful play of colours. They are 
extremely difficult to preserve or examine, except in 
the sea itself, on account of the large quantity of 

removed from the water, they rapidly dissolve, leaving 
scarcely a trace behind. 
Plate XXIX. fig. n. Medusa aurtta is one of 
the commonest species. It is a gregarious animal, 
and the pale blue umbrellas oscillate at times by 
hundreds on the waves, or are driven in shoals into 
bays and harbours. The young do not form a poly- 
pidom, but a single stem, from which the Medusz 
detach themselves. The separate stages of the Me- 
duse were formerly regarded as distinct animals, 
and described as such. — 
Fig. 0. Felagia panopyra is distinguished by 
its beautiful red colour, the length of its 8 marginal 
filaments, and its 4 slender oral tentacles. 
Fig. p. Cephea papuensis is remarkable for 
having each of the tentacles divided, so that the 
mouth is surrounded by 8 club-shaped appendages. 
Fig. q. Rhizostoma Aldrovandi represents a 
section of the Medusz in which there is no mouth, 
but the 8 tentacles exhibit apertures for the reception 
of microscopic nourishment. The rythmical motion 
of the umbrella is very conspicuous; and the urti- 
cating properties of this species render it very an- 
noying to bathers. 
Order Il. Siphonophora. 
These organisms are remarkable as occupying an 
intermediate position between a compound animal and 
an individual. In other compound animals (corals for 
example) the individuals resemble each other in ap- 
pearance and in organisation, but in the Szphonophora 
the separate animals of the colony perform different 
functions, and likewise change their appearance, thus 
sinking to the level of mere organs. The Szphono- 
phora are swimming compound animals, generally 
with a longitudinal axis, provided with a bladdery 
expansion above, to keep the stem upright. On the 
sides are placed the individual animals, with their body- 
cavities communicating with the cavity in the longitu- 
dinal axis. Some of the animals are bell-shaped, and 
assist in swimming, others are feeding animals, which 
possess a long thread set with urticating organs; and 
others again are medusa-like animals, which secrete the 
sexual products, and can detach themselves. The 
entire stem differs much in appearance according to the 
form, number and arrangement of the separate polypi. 
Order III. 
In this Order the polyp-state predominates. 
The Meduse which are produced from the eggs, 
either do not detach themselves at all from the poly- 
pidom, or if they do so, remain quite small. The 
stems are usually branched. 
Plate XXX. fig. b. Corymorpha nutans has an 
unbranched stem, attached by root-like processes. 
The small free Medusz are bell-shaped, and pro- 
vided with a long marginal thread. Our figure shows 
how they are placed in a circle round the mouth of 
the polyp, before they detach themselves. 
Fig. c. Bourgainvilia ramosa is a very deli- 
cate tree-like species The Meduse are placed like 
little buttons at the end of the twigs, from which 


Plate XXIX. fig. r. In Velella scraphidea the 
longitudinal axis is compressed to a flattened disc, 
on the under surface of which the separate polypi live. 
Fig. s. Diphyes gracilis is an elegant species 
with two large swimming-bells. Beneath them, at 
equal distances, hang the feeding polyps, with their 
long filaments, and the umbrella-shaped sexual polypi. 
Fig. t. Physala arethusa, the Portuguese Man- 
of-War, is one of the handsomest of the swimming 
polypi. The entire axis of the animal is expanded 
into a bulky horizontal bladder. The feeding polypi, 
which are situated on the bladder, have very long 
and strong filaments, covered with millions of urti- 
cating organs, which render the creature a very for- 
midable antagonist. 
Plate XXX. fig. a. Fhysophora disticha is fur- 
nished with a row of bell-shaped swimming polypi 
on each side, in addition to the bladder at the end 
of the longitudinal axis. 
Hydroida. 
they detach themselves, although in some 
closely allied species they remain fixed. 
Fig. d. Hydra viridis, the Fresh-water Polype, 
is a representative of almost the only fresh-water 
genus of the Cewlenterata. The few species of Hydra 
are generally fixed to floating objects, or to snail- 
shells. If a handful of duckweed 1s placed in a large 
glass, the little animals will soon be seen on the roots 
expanding a circle of tentacles. //ydra is famous 
for its tenacity of life, for it may be cut to pieces, 
and each fragment will become a new animal; or 
it may be turned inside-out like a glove without 
suffering any injury. It has no medusa-form, but 
reproduces itself by fission or eggs. 
very 
