INTRODUCTION. Vll 



floating members of the order, is totally destitute of a poly- 

 pary. 



Through the tubular cavity of the coenosarc the nutrient 

 matter, elaborated within the stomachs of the polypites, 

 circulates, reaching every portion of the structure and 

 supplying the elements needed to maintain the health and 

 growth of the whole. 



The circulation is of the simplest kind : a stream, bearing 

 along with it a multitude of restless granules of various 

 sizes, issues from the stomachs of the polypites and rushes 

 through the cavity of the coenosarc, pervading every portion 

 of the organism. After flowing downward for some time, 

 there is a pause in the circulation, and then the current 

 rushes back with great impetuosity, and, once more entering 

 the stomachs of the polypites, mingles with the contents. 

 A busy ferment takes place for some seconds in the diges- 

 tive sac, the larger particles hurrying to and fro amidst 

 the contained mass of food, until at length the efflux again 

 commences. The inner surface of the ccenosarc is covered 

 with vibratile cilia, and these seem to be the chief agents 

 concerned in maintaining the flow of the currents. 



Within the buds, which pullulate at certain points from 

 the common substance, and are developed into new poly- 

 pites, there is always a great aggregation of the nutrient 

 particles and a remarkable activity amongst them. They 

 crowd the cavity of the nascent polypite, and supply, as it 

 were, the building-material that is needed for the extension 

 of the structure. 



The coenosarc of the zoophyte may be likened to the 

 trunk, branches, and roots of the tree, regarding the latter 

 merely as a means of attachment to the soil. The zooids 

 which it supports and binds together in one organic whole 



