2 POLYZOA. 



example,* wliicli is a fair type of the Class, we find 

 an animal living freely in its cell, with whose 

 walls t it is connected only by means of muscle- 

 bands and threads, at certain points, and by the 

 covering of the mouth of the cell. This covering 

 is membranous, and is capable of great protrusion ; 

 the animal, in the process of expansion, pushing 

 out a doubling of the membrane, like the turning 

 inside-out of a stocking. The animal has a receiv- 

 ing orifice or mouth, surrounded by a crown of 

 tentacles, and leading into a sensitive and con- 

 tractile gullet, into which the food is gorged ; 

 thence it passes into a capacious crop, and after- 

 wards into a muscular gizzard ; to this succeeds a 

 duct leading into a digesting stomach, whence a 

 long intestine passes upward, emerging by a dis- 

 charging orifice close to the receiving one. 



This highly developed digestive system is cha- 

 racteristic of the Class, as well as this course which 

 it follows — a line bent upon itself; the only de- 

 viation of importance being that, in some genera, 

 the muscular gizzard is either wanting or indis- 

 tinctly developed. 



The tentacles differ importantly from those of 

 the Polypes. Instead of being soft, fleshy, highly 

 contractile, and studded with knots of nettling- 

 capsules, they are straight, somewhat stifi*, slender 

 threads, incapable of contraction, and set, on their 

 two opposing sides, (viz., on those sides which 

 face the next tentacles,) with long cilia_, the action 

 of which is to produce a strong current up one side 



* Figured and described in detail in my " Devonshire Coast," 

 p. 132, by the name of Eiicratea ckelata. 



+ Perhaps it would be more correct to say, with a vascular 

 coat which lines the walls of the cell. 



