POLYZOA. 5 



posing animal substance in water invariably at- 

 tracts crowds of infusory animalcules, which then 

 breed with amazing rapidity so as to form a cloud 

 of living atoms around the decaying body, quite 

 visible in the aggregate to the unassisted eye, and 

 these remain in the vicinity, playing round and 

 round until the organic matter is quite consumed. 

 Now, a tiny Annelid or other animal, caught by 

 the bird's-head of a Polyzoan and tightly held, 

 would presently die ; and though in its own sub- 

 stance it would not yield any nutriment to the 

 capturer, yet by becoming the centre of a crowd of 

 busy Infusoria, multitudes of which would con- 

 stantly be drawn into the tentacular vortex and 

 swallowed, it would be ancillary to its support, 

 and the organ in question would thus play no 

 unimportant part in the economy of the animal. 



Besides the birds'-heads (avicularia] , some spe- 

 cies are furnished with long slender whip-like, 

 spines (vibracula), likewise moving freely on a 

 hinge-joint, and apparently serving to rid the 

 animal of intruding vagrants, and to cleanse away 

 accidental defilement, by sweeping across the ori- 

 fice of the cell. Both these kinds of organs, by 

 their presence or absence, their form, position, &c., 

 furnish aids to the determination of genera. 



The entire assemblage of cells springing from 

 one root-thread, or originating from a single cell, 

 is called the polyzoary. 



The reproduction of the species, so far as it has 

 been yet observed, is by means of ovules, or soft 

 eggs, generated within special cells, which are 

 ordinarily situated on the summit of a dwelling- 

 cell. The egg when discharged resembles an 

 infusory animalcule, being a minute opaque body, 



