BIRD'S-HEAD PROCESS, OR ATICULARIUM. 445 



seldom 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. 



Fig. C. is another species belonging to the same genus, and is remarkable for the 

 long pointed spines that project from the margin, like a pair of cow's horns. In allu- 

 sion to this peculiarity it is called CatenieeUa corniita. 



At rig. I) is shown another curious polyzoon, termed Calpidium ornaium, also found 

 in Bass's Straits, at the same depth as the preceding species. A magnified figure is 

 given at E, in order to show the singular method of its construction. 



As the reader may observe, each cell is extremely wide in proportion to its depth, and 

 instead of possessing but one mouth, is pierced with three apertures shaped something 

 like keyholes. It is conjectured that each cell is inhabited by three separate individ- 

 uals, 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 dis- 

 covered, although some remains, apparently of the inhabitants, 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 given at fig. F, where the Sali- 

 cornaria farciminoides is represented of the natural size. The strange specific 

 name of this creature is given to it on account of its external resemblance to the Far- 

 ciminaria, 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 

 subdivision 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 being called Hippocrepia or Horseshoe animals, 

 because the tentacles are arranged in a shape resembling that of a horseshoe. It will 

 be, perhaps, hardly necessary to apologize for the introduction of so many technical 

 terms, the fact being that the minute dimensions of the objects have caused them to 

 escape popular observation, and to depend for their nomenclature upon the learned 

 and scientific. Still, the technical phraseology is never employed where its use can 

 be avoided, and when circumstances render its introduction inevitable, its meaning and 

 the reasons for its employment are always given. 



We now arrive at another family, the Cellularidas, where the general shape resembles 

 that of the preceding family, but the cells, instead of being arranged round an imagi- 

 nary axis, and so forming cylindrical branches, are arranged on the same plane. Fig. 

 H is a magnified example of this family, the Cellularii Peachii, so called in honor of 

 the eminent naturalist, Mr. Peach. 



At fig. I is shown the mouth of a single cell, belonging to the genus Menipea, found 

 in Tierra del Fuego, and termed from its habitat, Menipea Fuguensis. The object of 

 giving this example is to show the curious "operculum " which closes or rather guards 

 the mouth of the cell, and in this genus is in the form of a simple spike. This species 

 is" found at low water. 



At fig. K we have good examples of the avicularia and vibracula, already mentioned, 

 and this species has been chosen on account of the enormous dimensions of the forme 

 organ, which is nearly as large as the cell to which it is attached. Many instances of 

 the avicularia will be seen in the succeeding plates. 



The avicularium is an object which is set somewhere about the middle of a cell, 

 and always upon its outside, and assumes various shapes in the different species of 

 polyzoa. What may be the precise nature of the avicularia is at present rather a 

 mystery, and no one can definitely pronounce them to be actual portions of the cell, or 

 merely parasites that remain affixed to the same spot. In all cases there is a decided 

 resemblance to the head of a bird, though in some species the similitude is closer than 



