ORDER ACTINOIDEA. 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 
Srom the side of a stem or branch. 
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 Gorgonie afford illustrations of this. 
Other examples of furcation are connected with terminal budding. 
b. Branching by lateral shoots. Yn 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 
