BRYOZOA. 



95 



complex digestive apparatus is developed for the service of an organ- 

 ised being as immovable as the plant which is rooted in the soil- 

 But we shall, hereafter, meet with animals of higher grade of 

 organisation than the Bryozoic polypes, as the Barnacle, the Oyster, 

 and the Spondylus, which are equally fettered to the spot on which 

 they grow, and which more strikingly demonstrate how secondary 

 a character of animal life is mere locomotion. 



The complicated and characteristic condition of the alimentary 

 canal in the Bryozoa was discovered independently, and nearly about 

 the same time, by Ehrenberg, Milne Edwards, and Dr. V. Thompson. 

 The ciliated structure of the arms was observed by Steinbuch and 

 Dr. Fleming. The ciliated gemmules, and their development, have 

 been well described in the Flustra carbesia by Dr. Grant. All these 

 observations have received a welcome confirmation, and many highly 

 interesting facts in the organisation and properties of the Bryozoa, 

 have been added, by Dr. A. Farre ; a careful perusal of whose ad- 

 mirable Memoir in the Philosophical 

 Transactions for 1837*, will amply 

 repay the reader. 



Most of the Bryozoa are micros- 

 copic ; but, being composite or aggre- 

 gated animals, they sometimes form 

 sufficiently conspicuous masses. The 

 most familiar and common species con- 

 stitute the substance called sea-mat 

 (^Flustra), which incrusts, by its little 

 hexagonal cells, as by a delicate mo- 

 saic pavement, sea-weed, shells, and 

 other marine bodies. The calcareous 

 sea-mat is called Eschara. Some spe- 

 cies rise from their surface of attach- 

 ment and form amorphous masses, like 

 sponge ; or are regularly and delicately 

 ramified, like the little hydriform co- 

 rallines. 



Each polype presents an oblong de- 

 pressed, or elongated and cylindrical 

 figure, and is protected by a dense in- 

 tegument in the form of a cell or case 

 (Jig. 5\. a, a), to the mouth of which 

 is attached a sac (b, b) composed of 



Bowerbankia. 



* P. 387. plates xx. to xxvii. 



