87 



ing to some distance down the sides ; having several small 

 round perforations arranged without any regular figure . body 

 of considerable breadth and often nearly twice the height of 

 its diameter. 



The peculiar arrangement of the plaits and head in the last 

 two species rendered any anastomosis of adjoining plaits not 

 essential in either of them. The much greater height of the 

 present species rendered occasional points of anastomosis an im- 

 portant means of securing the permanence of the position of the 

 folds. The width and depth of those folds rendered a large 

 head necessary, while it made unnecessary any large single cen- 

 tral cavity ; the several small openings in the head giving suffi- 

 cient access to the sea-water for the purpose of bathing freely all 

 the internal surface of the polypiferous membrane. The unity 

 of form * is not in the least degree impaired by the existence of 

 these several points of access. The one head still holds in place 

 all the several plaits, a contrivance for the security of the entire 

 animal and of the individual polyps wholly different from that 

 which is found in every species of the family Brachiolites. 



In all the various and so greatly varying forms which have 

 been thus seen to be included in the genus Cephalites one end is 

 found to be subserved, namely, the maintenance of the security 

 of the whole mass, and of each individual of its myriads of living 

 tenants ; together with the unimpeded access of the sea-water 

 that element upon whose constant presence the life and subsist- 

 ence of those myriads depended. The great diversity is no less 

 striking than is, in each case, the completeness of the varying 

 methods which nature has adopted for securing that ever-teeming, 

 ever-active life which excites the inquirer's increased admiration 

 at every step he takes. 



Genus BRACHIOLITES. 



Character. Shape and size very various, but always much lobated 

 or branched : internal cavities of lobes and branches always 

 communicating : extremities closed or open : membrane form- 

 ing the wall sometimes plain sometimes folded : margin of wall 

 thinned or rounded off to an edge: membrane of wall poly- 

 piferous on both external and internal surfaces. 



Departing altogether from the forms hitherto examined, the 

 present genus is characterized by its lobated or branched divi- 

 sionsf. These divisions communicate internally, either by open- 



* See before, p. 58 note. 



f Sec pp. 51, 57 note J, and 85. 



