BRYOZOA. 145 



also an oesophagus for deglutition, an intestine for the separation 

 of tlie nutrient chyle, and a distinct external outlet for the indi- 

 gestible refuse of the food : it may possess a stomach with strong 

 muscular walls and a deutated lining for trituration, and a second 

 stomach with glandular walls for digestive solution or chymification, 

 and thus present an alimentary canal as complicated and as highly 

 elaborated as in the bird. Yet the microscopic polypes Avhich 

 manifest this high condition of the digestive apparatus are fettered 

 to the spot, where, as ciliated gemmules, they finally rested after 

 their brief early locomotive stage: the complex digestive appai'atus is 

 developed for the service of an organised 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 

 6. g. the Barnacle, the Oyster, and the Spondylus, which are equally 

 fettered to the spot on which they groAv, and whicli 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 discovei'cd independently and nearly about 

 the same time, by Ehrenberg*, by Audouin and Edwardsf, and by 

 Dr. V. Thompson.:}: The ciliated structure of the arms was observed 

 by Steinbuch § and Dr. Fleming. || The ciliated larv^, and their 

 place of 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 admirable Memoir in the 

 Philosophical Transactions for 1837**, will amply repay the reader. 



Most of the Bryozoa are microscopic ; but, being composite or 

 aggregated animals, they sometimes form sufliciently conspicuous 

 masses. The most familiar and common species constitute the 

 substance called sea-mat (^Flustra), which incrusts, by its little 

 hexagonal cells, as by a delicate mosaic pavement, sea-weed, shells, 

 and other marine bodies. The calcareous sea-mat is called Eschara. 

 Some species {Halodactylus) rise from their surface of attachment 

 and form amorphous masses, like sponge ; others ( Vesicularia^ 

 Valkeria, Serialaria, Cellularia) are regularly and delicately rami- 

 fied, like the little hydriform corallines. 



* CXXXni. Bryozoa " ore anoquc distinctis tubo cibario perfecto." 

 t CXXIV. p. 13. X CXXIII. 



§ CXXV. p. 89. II CXXVI. p. 488. pi. xv. fig. 1. c. 



^ CVIII. p. 116. - ** XXXV. p. 387. plates xx. to xxvii. 



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