362 POLYZOA. 



adhering to sticks, stones, or leaves, or even lying freely in the water ; others being flat and 

 ramified, like broad-leaved sea-weeds ; others spreading film-like over leaves, stones, shells, or 

 similar objects ; while a few are able to crawl at liberty, the entire organism being animated 

 by some wonderful instinct, which urges all the myriad individuals of which it is composed to 

 employ their force in the same direction. 



The number of these creatures is so vast, that it is impossible to give more than a brief 

 description of them ; but in the following pages it will be found that a careful selection has 

 been made of the typical forms, and that sufficient details of their structure will be given to 

 enable the reader to form a general idea of the subject, and in most cases to refer any speci- 

 mens which he may find to their genera or families. Those who desire further information on 

 the subject will find it in Busk's elaborate catalogue of the Marine Polyzoa, and the large 

 work by Allman on the Fresh-water Polyzoa. 



Putting aside the classification of the polyzoa until the termination of the work, we will 

 proceed at once to the description of the many species of this class. 



The first family of the polyzoa is known by the manner in which the cells are arranged 

 around an imaginary axis, and connected with each other by flexible stalks. The general 

 shape of the whole group, or " polyzoary," as it is termed by some authors, is very shrub-like, 

 standing boldly erect, and giving out branches by two and two, after the fashion called by 

 botanists " dichotomous." 



An example of one of these beings, the LITTLE CHAIN, or BREAST-PLATE, is plentifully 

 found in the sea, and is properly classified among the zoophytes. The Catenicella hastata is 

 somewhat remarkable for the shape of the cells, the form of their mouths, the method in 

 which they give out their branches, and the peculiar organs called technically "avicularia" 

 and "vibracula;" the former being processes that in many species bear an almost absurdly 

 close resemblance to the heads of birds ; and the latter, curious hair-like projections, which 

 move regularly backward and forward as if impelled by machinery. These remarkable organs 

 will be presently described more fully. 



The members of the present genus are found most commonly in the Australian seas, sel- 

 dom in the southern hemisphere, while in the northern hemisphere they are almost entirely 

 unknown. Many specimens have been taken from Bass's Straits, at a depth of forty -five 

 fathoms. As a general rule, however, the polyzoa prefer the shallower waters, and are most 

 commonly found a little below low- water mark. 



Another species belonging to the same genus is remarkable for the long pointed spines 

 that project from the margin, like a pair of cow's horns. In allusion to this peculiarity it is 

 called Catenicella cornuta. 



Another curious polyzoon, termed Calpidium ornatum, is also found in Bass's Straits, at 

 the same depth as the preceding species. It shows a singular method of construction. 



Each cell is extremely wide in proportion to its depth, and instead of possessing but one 

 mouth, it is pierced with three apertures shaped something like keyholes. It is conjectured 

 that each cell is inhabited by three separate individuals, a supposition which is strengthened 

 by the great comparative dimensions of the cell and the thickness of its walls. Still, no sign 

 of internal partitions have been discovered, although some remains, apparently of the inhab- 

 itants, have been seen at the bottom of the cell. In some cases there are only two apertures to 

 each shell. 



An example of the typical genus of this family is the SaUcornariafarciminoides. The 

 strange specific name of this creature is given to it on account of its external resemblance to 

 the Farciminaria, another genus of polyzoa which will be presently described. In this genus 

 the cells assume a kind of honeycombed aspect, being almost hexagonal in their shape and 

 pressed closely together. 



In this place it may be as well to mention that in all the species belonging to the first sub- 

 division of the polyzoa the mouth is not quite at the extremity of the cell, is of a somewhat 

 crescentic form, and furnished with a movable lip or door, which closes the aperture when the 

 animal retreats. In many cases this lip is membranous. All the marine polyzoa are termed 

 Infundibulata, or Funnel-shaped animals, on account of their form ; their fresh-water relations 



