70 



ZOOPHYTES. 



Fig. 31. 



the branches have no one polyp at apex more prominent than the 

 others. In the Madrepores, a spiral arrangement of the polyps may 

 sometimes be distinguished, resulting from some 

 regularity in the developement of buds, in turn, 

 from the different sides of a parent-polyp. 



72. A periodicity in the budding process is 

 well illustrated in the jointed corals of the Gor- 

 gonia family. The Meliteeas form foot and 

 tissue secretions, like the true Gorgonia? ; but, 

 instead of having the former as an axis, within 

 the others, the two appear to constitute alter- 

 nating joints. This may be accounted for by 

 supposing the budding to be periodical at the 

 apex of the branch, the new buds adding to the 

 extremity, first, their foot-secretions, and then 

 their tissue-secretions. 



73. It is obvious that the form and position of 

 the growing stems must also depend on the sym- 

 metrical or unsymmetrical production of buds. 

 The stem will be cylindrical when the buds are 

 equal and open alike in every direction. If they 

 form only in two opposite directions, in a single 

 series, we have a zoophyte with two-edged 



branches, as in some PterogorgiiE.* Or if the buds opening in two 

 directions spread sidewise, instead of forming a simple vertical series, 

 the zoophyte produced is an erect plate, with polyps opening on the 

 opposite surfaces, as in some Milleporse. 



When the budding is unstjmmetrical, the zoophytes formed are 

 oblique or horizontal. The buds, having an oblique tendency, may 

 pass off at a different angle on opposite sides, or elongate more rapidly 

 on one side than the other, or they may be confined to one side alone. 



Cylindrical stems, in consequence of this oblique or unsymmetrical 

 mode of budding, become horizontal, as in many Madrepores ; the 

 buds open equally in every direction, but elongate most rapidly on 

 one side of the branch in a horizontal direction. By this mode of 

 increase, the vase Madrepores are produced, f some of which are several 

 feet in diameter. 



A few remarks may be added upon the mode of branching in these 



Dendrophyllia. 



* The Gorgonia anceps and other species with seriate polyps. f See plates 32 and 33. 



