68 ZOOPHYTES. 



arrangement of the polyps around the branch, especially apparent at 

 the apex. The spire, in some species, goes aroiind by the right, and, 

 in others, by the left ; and a single circuit of the spire appears to 

 contain five polyps, though with some irregularity. In figure 31, 

 this mode of arrang-ement is seen in an end view of a branch enlargr-ed. 

 The calicles are numbered, to show their relative positions, com- 

 mencing with the apical as number 1. At the same time that the 

 figures exhibit the spiral order, they also indicate the fact stated, that 

 there is some irregularity in this arrangement. 



2. Lateral budding, with acrogenous gro7Vth, in the pohjps. 



68. When polyps have the upward mode of growth, different forms 

 result, according as the budding power is general throughout the zoo- 

 phyte, or belongs only to a limited number of polyps, — the older 

 individuals losing the power by age. 



69. Unlimited symmetrical budding. If each polyp, as soon as pro- 

 duced, buds like the parent, and retains this power indefinitely, or 

 without limit, the zoophyte will necessarily take on globular or 

 hemispherical forms ; for increase, in such a case, takes place equally 

 in every direction. There are certain species among the massive 

 Porites, in which these forms thus result. Yet, owing to a slight 

 irregularity, or the more rapid developement of buds in some parts 

 than others, these zoophytes have generally a form irregularly glome- 

 rate, rather than symmetrically globular. 



Globular or hemispherical forms are produced in the same manner 

 among the segregate, as the massive or aggregate zoophytes. The 

 Columnaria; are examples of species consisting of adnate prisms. In 

 the Tubipores, the polyps form, by their secretions, parallel tubes, 

 which, as they grow and give out buds from their sides, necessarily 

 diverge a little, and a convex or hemispherical form is the result. 

 The tubes are united at intervals by transverse plates, which are 

 formed at the budding process, as is apparent from the fact that the 

 buds proceed from these plates; and the internal cavity may be 

 traced into them, though very much reduced in size. The process of 

 bi;dding is similar to that of the Aulopora, except that the polyps 

 have an acrogenous growth, and bud periodically as they grow up- 

 ward ; and, moreover, the buds, at the time they are given out, 

 coalesce laterally into a plate, like the Xenise, instead of forming a 

 network : after this coalescence, they lengthen upward between the 

 other polyps, and thus add new tubes to this "organ-pipe" coral- 

 zoophyte. 



