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P0H7LAR SCIENCE REVIEW. 
intervals along the stem and branches, and the reproductive 
capsules are unprotected. In the other principal section, the 
calycles are ranged close together in a continuous series, and 
the polypites can withdraw themselves wholly into their little 
dwellings ; the “ calicetti ” are disposed in definite and constant 
order round the calycles, and the reproductive capsules are 
either collected in groups and inclosed in a pod-like case, or 
all but universally associated with some kind of protective 
appendage. In Plate CX., fig. 1, a member of this section is 
represented, and a glance at it will show that, however it may 
differ in minute structure from the form which I have just 
described, it presents the same general habit, and is as con- 
spicuous for grace of figure and delicacy of detail. Two of the 
ribbed and crested cases which shelter the reproductive capsules 
are shown standing out from the mid-rib amongst the pinnae, and 
will at once attract attention from the singularity of their form. 
A familiar member of this section of the Plumularian group 
is the common “ Podded Coralline,” which overspreads some of 
the larger Fuci, covering them with its network of fibres, and 
hanging on every spray a multitude of its amber plumes. What 
masses I have seen of the “ podded weed ” ( Halidrys siliquosa) 
invested throughout by this elegant hydroid, overgrown by the 
ramifying thread, which had pushed its way over stem, branch, 
and branchlet, and sent up at all points hundreds of the plumous 
shoots, each of which bore aloft a company of polypites, a vast 
parasitic population ! 
Such a commonwealth is a wonderfully complex unity ; a 
single germ its origin ; a single life pervading it ; thousands of 
quasi independent elements included in its manifold individu- 
ality. A single plume of A. pennatula (PL CX., fig. 3) of 
moderate size may bear some fifteen hundred hydrse ; and a 
plume is but one state of a great federation. Dana reckons the 
number of polypites on a single specimen of a large foreign 
species, which reaches a height of three feet, at not less than 
eight millions ; and this is but a pigmy compared with the 
gigantic form from the Pelew Islands, described by Semper, 
which attains a height of five or six feet and spreads as a 
veritable forest over the bed of the sea. 
We are not acquainted with many variations upon the Plumu- 
larian type ; the family has hitherto included few genera, but 
the number will probably increase considerably as we become 
more familiar with the modifications of the reproductive system. 
Two of the sub-groups I have already briefly characterised ; 
in the u Sea-beard ” ( Antennularia ), one of the commonest 
waifs on our sandy shores, the pinnse are ranged round the stem 
in whorls, and the plumose appearance is lost. The divergence 
from the normal arrangement in this case is apparently great, 
