BIED'S-HEAD PEOCESS, OR AVICULAR1UM, 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 allusion 

 to this peculiarity it is called Catenicella cornuta. 



At iig. D is shown another curious polyzoon, termed Calpidium ornatum, 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 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 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 

 Salicornaria fardminoides 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 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 

 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 tiiw 

 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 Cellularidte, where the general shape resembles 

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

 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 honour 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 Fuyuensis. 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 former 

 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 in. others. Onlv 



