THE DISCOPHOEES, OE LAEGE MEDUSiE. 125 
a striking feature of the organism ; it is kept in frequent mo- 
tion, as if on the watch for prey, and is often thrown wide open, 
so that every recess of the capacious stomach becomes visible. 
The polypite is very protean in shape, and never long the same. 
As it feeds and attains its full proportions, its vegetative 
powers begin to manifest themselves; young sprout from 
various parts of the body, as in the Hydra, and several gene- 
rations are at times organically united ; long, thread-like 
shoots are also cast out, from which new polypites are deve- 
loped, and soon the primary zooid is the centre of an extensive, 
colony that has literally grown out of its own substance. 
But as the seasons change it enters upon a new phase of its 
being; the production of polypites like itself ceases, and a 
new developmental process sets in. The body, which is now 
large and cylindrical, begins to divide across ; first a constric- 
tion a little below the tentacles, then another a little below 
this (Plate LXX. fig. 5), then another, and so on till the whole 
is partitioned into transverse segments, with the exception of 
a small portion of the base. The constrictions deepen ; each 
segment becomes more and more independent, while its margin 
is cut into prominent, sinuated lobes, which show like 
frills on the surface of the now disintegrated body. In this 
state the structure presents the appearance of a pile of circular 
discs ; or we may compare it, with Agassiz, “ to a string of lilac- 
blossoms, such as the children make for necklaces in the spring.” 
But the polypite is not to lose its identity. Immediately 
below the lowest segment a new circle of tentacles is developed 
(Plate LXX. fig. 6&) ; about the same time the original set at 
the top is absorbed and disappears ; * the segments, now con- 
nected by the slightest link, begin to manifest independent 
vitality, and exhibit the contractile movements so charac- 
teristic of the Medusae. After a term of vigorous struggles the 
uppermost frees itself from its connection with the polypite, 
and the rest soon follow. The basal portion, with its new wreath 
of arms, survives. The detached segments, reversing their 
position in the water, present the pulsating disc of the Medusa, 
with its lobed margin and circle of eyes, and take to the cus- 
toms of free oceanic life (Plate LXX. figs. 8 and 9). Let us 
pause for a moment to consider the significance of this course 
of development. The polypite of the Discophore, after multi- 
plying itself indefinitely by gemmation, proceeds to fulfil its 
most important function in maturing certain highly specialised 
reproductive buds, which it casts loose at a certain point of 
their development, to lead an independent life and prepare 
and distribute the seed of new generations. We have a parallel 
Van Beneden’s " Polypes,” pp. 80, 81. 
