168 ZOOPHYTES OF GUERNSEY. 



wliile the flower-like adult, with its branched stem profusely 

 studded with polyp-stars, is to all outward appearance a 

 plant. 



Passing on now to the Polyzoa, we shall see that, not- 

 withstanding their likeness to the Hydroida, they are entitled 

 to a much higher rank in the scale of animal life. In both 

 cases the little polyp bears a crown of tentacles, but in the 

 Hydroida these tentacles are soft, fleshy, contractile, and 

 studded with knots of stinging ca])sules ; whereas in the 

 Polyzoa the tentacles are stiff, slender threads incapable of 

 contraction, but furnished with vibratile cilia which, when the 

 animal is expanded, produce by their incessant wave-like 

 movement a current which sweeps any ])assing animalcule, or 

 floating particle of food, into the vortex of the mouth. This 

 ciliary covering of the tentacles serves at once to distinguish 

 the Polyzoa from the Hydroids. But in addition to this the 

 tentacles also act as respiratory organs, and perform the 

 function of gills. 



Unlike the simple digestive sac of the Hydroids, the 

 Polyzoa possess a very complex alimentary system, which may 

 be compared to that of some of the higher animals The 

 mouth leads through the oesophagus into a contractile gidlet, 

 where the food is gorged ; thence it passes into a capacious 

 crop ; and in some cases there is a muscular gizzard. From 

 this gizzard a duct leads into the digestive sac, whence a long 

 intestine passes upwards, and ends in the anal orifice. The 

 muscular system of the Polyzoa is a complicated one ; and 

 there is, in certain species at any rate, a simple and rudi- 

 mentary nervous system, consisting of a single ganglion which 

 sends out sets of nerves in different directions. 



Many genera among the Polyzoa are characterized by 

 the possession of certain curious accessory organs termed 

 amcvlaria^ or " bird's head processes," which are in some 

 respects similar to the pediceJlarim of Sea Urchins and Star- 

 fishes. The precise function of these appendages has not been 

 clearly determined, but they are remarkable by their striking 

 resemblance to the head of a bird, being furnished with two 

 mandibles, the upper one of which is fixed, and the lower one 

 movable. During life these processes are in continual motion, 

 opening and snapping their jaws with great vigour, and laying- 

 hold of any minute objects which come within their reach. 



Another singular appendage, quite different in form and 

 function from the avicularia, is met with in a few genera, but 

 it is of comparatively rare occurrence. It consists of a long 

 whip-like bristle, termed a vihracnJum^ which sweeps round at 



