SQUIRTS, POLYPS, AND JELLY- FISHES. 59 
under the name of sea-fir, sea-moss, or Sertularia 
(Pl. 4, Figs. 7, 10), are, indeed, far removed from 
plants, and even far above the 
lowest forms of animal life. 
To those who are acquainted 
with the little polyp of our 
fresh-water streams and ponds, 
the hydra, it is but necessary 
to say that the sea-fir is prac- — Potyr or Serrunarra, 
tically only a compound colony rit A 
of this animal, which has become covered over by, or 
encased in, a horny sheath. Cast your eye over a 
single twig of the Sertularian, and note the minute 
scale-like bracts which run off at an acute angle 
with it. These, when magnified, are seen to be 
hollow sheaths or cups (thec), each of which, 
during the life of the animal, contained a minute 
polyp, to all intents and purposes identical with 
the hydra. The different polyps were united 
with one another by means of a common stalk 
which occupied the centre of the connecting axis 
or twig. But what is the polyp itself? A hollow 
little body, with an opening at one end, the mouth, 
and a circle of hollow arms or tentacles, an out- 
growth of the body-cavity itself, surrounding the 
mouth. It might be likened to a glove closed at 
the bottom, and with a single rupture (correspond- 
ing to the mouth of the polyp) at the base of one 
of the fingers. This colony has become compound 
through repeated budding, the individual polyps 
after they have once budded out contributing by 
way of nourishment to the welfare of the commu- 
