MOLLUSC A. 53 



Order 1. Bkyozoa. This name was imposed by Ehrenberg, who was 

 one of the first to demonstrate the true nature of them. They are small 

 animals, aggregated in great numbers, like coralligenous zoophytes, having 

 a distinct stomach and an intestine curved upon itself, with an outlet near 

 the mouth. An analogy with the Cephalopoda is apparent in the tentacles 

 which surround the mouth, and which are covered with vibrilhe. These 

 vibrilla3 cause currents of water which bring the animalcula within reach, 

 which serve as food. The tube into which the animal withdraws varies in 

 texture, being membranous, horny, fibro-gelatinous, or calcareous. This 

 tube corresponds to the outer tunic of the Tunicata, in being in organic 

 connexion with the interior parts, even the calcareous matter of the harder 

 kinds being deposited throughout the membranous tissues. Each tube is in 

 contact with its neighbors, sometimes to the number of many thousands. 



Dr. Farre thus describes the tube or cell in the Yesicularida3 : " The 

 transparent horny cell which closely embraces the body of the animal, is 

 nearly unyielding in its lower two thirds, but terminates above by a flexible 

 portion, which serves to protect the upper part of the body when the whole 

 is expanded, in which state it is of the same diameter as the rest of the cell, 

 but, when the animal retracts, is folded up, and drawn in after it, and 

 completely closes the mouth of the cell. The flexible part consists of two 

 portions, the lower half being a simple continuation of the rest of the cell, 

 the upper consisting of a row of delicate bristle-shaped processes or seta, 

 which are arranged parallel with each other around the top of the cell, and 

 are prevented separating beyond a certain distance by a membrane of 

 excessive tenuity, which surrounds and connects the whole. This mode of 

 termination of the cell is one of constant occurrence, as will be described 

 in other species, and is evidently a provision for allowing of the freest 

 possible motion of the upper part of the body in its expanded state, to which 

 it affords at the same time support and protection." — Pldl. Trans.^ 1837, 

 p. 393. 



Johnston thus describes the habits of some of these animals : " Let 

 us now suppose that the polypes are in a state of extrusion, and fully 

 expanded, all the cilia in play, and the water whirling in rapid streams up 

 and down the opposite sides of the tentacula, carrying with them nutriment 

 and the breath of life. All is quietness and security around, and the little 

 creatures are evidently in a state of happiness and enjoyment ; no one who 

 has witnessed the microscope scene (the myriads of the little flosculous 

 heads that pullulate and blossom over the entire polyj^idom, as thickly 

 peopled as the swarming hive) can have any doubt of this, especially when 

 he remarks the acuteness and vivacities of their sensibilities and actions ; for, 

 under his eye, one will ever and anon suddenly sink out of view, hide itself 

 within the cell, again on a sudden emerge and expand, or, it may be, lay 

 itself down in repose and concealment, until digestion has freed it from a 

 state of repletion, or forgetfulness has removed the alarm of an enemy. 

 These positions are assumed with such rapidity, that the eye cannot trace 

 the steps of the process, and large glasses and minute skill are required to 

 reveal to us its mechanism." — Brit. Zooph.^ p. 241. 



ICONOGRAPHIC ENCYCLOP.-EDIA. VOL. II. 17 257 



