ORDERACTINOIDEA. 71 



corals, before we proceed to consider the peculiarities of growth con- 

 nected with terminal budding. 



74. There are two modes of branching: — 1. By a simple furcation 

 of the extremity of a branch; and, 2. By the sprouting of a branch 

 from the side of a stem or hranch. 



a. Branching by furcation. Furcation of the summits occurs in 

 species which grow by means of a parent-cluster of polyps. It gene- 

 rally proceeds from the accumulation of buds, and the consequent 

 enlargement of the extremity. The budding of polyps in the midst 

 of a budding cluster causes a slight divergence between them, in- 

 asmuch as the budding goes on more rapidly than the elongation of 

 the branch. The extremity consequently enlarges a little, and, 

 beginning in this way to exceed the normal breadth of the budding- 

 cluster, furcation commences. The central polyps at the apex lose 

 their budding powers after attaining a certain age, and, as the cluster 

 is thus divided, each part goes on lengthening independently. This 

 effect may be due to the fact that the zoophyte is able to sustain 

 only a budding cluster of a certain size; a variation in the amount 

 of nutriment or other causes affecting the vitality of a species, 

 appear, however, to vary this size, and many irregularities in the 

 same specimen may be traced apparently to this cause {\\ 84, 85). 

 It is not possible generally to detect a periodicity in the deve- 

 lopement of buds causing the furcation. Yet it is apparent in 

 some instances in which the stem retains its cylindrical form for a 

 considerable length, and then rather abruptly enlarges and subdi- 

 vides. In all instances, there is much uniformity in the frequency of 

 furcation, or the length, of a branch before the process begins. The 

 forms resulting from this mode of branching are crowded cespitose 

 clumps, and have rarely the arborescent shapes, common where 

 branching takes place by lateral shoots. 



When the polyps of a parent-cluster rapidly elongate, the cluster 

 does not enlarge at apex, and such species, therefore, cannot branch 

 by furcation. The Gorgoniee afford illustrations of this. 



Other examples of furcation are connected with terminal budding. 



b. Branching by lateral shoots. In species which branch by lateral 

 shoots, the process of branching depends generally upon the capa- 

 bility of certain polyps, below the summit, to become, after a 

 certain time, budding polyps. The growing stem of a Madre- 

 pore would retain unchanged its simple cylindrical form, were it not 

 possible that some of the polyps below should develope gemmating 



