THE POLTZOA. 
59 
pharyngeal chamber (fig. 1, c). From this, by powerful con- 
tractions, they are shot down the oesophageal tube (fig. 1, d), 
either into a gizzard (fig. 1, e), where they are triturated, or, 
in the absence of this organ, directly into the stomach itself 
(fig. 1, /), a bag or sac, which is usually of a rich reddish- 
brown colour, and, with the rest of the viscera, is suspended in 
the cavity of the cell. Here they are rapidly digested. The 
unuseable portions are sifted out and borne by the action of 
cilia towards the upper end of the stomach, which has the 
appearance of being doubled upon itself; and, after rotating 
here for a time, they pass through a valvular orifice (fig. 1, g) 
into the intestine (fig. 1, h), a long and slender tube which is 
continued upwards to an outlet at the base of the tentacles. 
The space that intervenes between the body of the polypide 
and the walls of the containing cell (the 'perivisceral cavity) is 
filled with fluid, into which the products of digestion find their 
way, it is supposed, through the walls of the stomach, and are 
thus made available for the nutrition of the common life. In 
this cavity the reproductive organs are developed at certain 
seasons of the year. 
The polypides are lively and rapid in their movements ; and a 
most interesting sight it is to see them issuing from their little 
dwellings, and suddenly expanding their exquisite bells of ten- 
tacles, clothed with a thousand vibrating cilia, and then on the 
slightest alarm darting back again with the speed of light. A 
well-developed muscular system supplies the means of all this 
activity. 
A simple nervous system has long been recognised in each 
polypide, consisting of a single ganglion placed between the 
oesophagus and the rectum, from which filaments pass off in 
various directions, and especially, it would seem, towards the 
tentacular region.* Such is the general plan of structure. 
It is impossible to frame any general description of the 
aspect and habit of the Polyzoa . These are as various as 
the modes of gemmation. They grow in plant-like tufts, 
stem and branches composed of series of cells linked together ; 
they spread like lace-work, or as fairy chains, over other bodies ; 
they rise into stony coral-like masses ; they cover the fronds of 
the seaweed with fleshy crusts or silvery network ; they form 
colonies of exquisite little frosted tubes. In many of the stony 
kinds the cells are richly sculptured, the single genus Lepralia 
exhibiting an immense variety of microscopic ornament. 
* Nitsche, in an able and interesting paper on the fresh-water Polyzoa, 
has described and figured an ample and most effective service of nerves in 
the lophophore of the well-known Alcyonella. 
