Protandry and Senescence in Corals. 465 
than from the cutting off of masses of the central polyp by its 
advancing epithaeca. The presumption at present — from the 
large number of specimens dredged by Semper — is that these 
small polyps were formed in the latter manner. With knowledge 
of some of the facts alone — and none of the possible causes — this 
form must be deemed to represent a third variation. 
The polyps appear to give reliable characters of the species of 
the genus. In consideration of this and the definite existence 
of about 3 per cent, of intermediates, the three so-called species 
must be deemed to be varieties of a single species. This is the 
first suggested case of discontinuous variability in the Madre- 
poraria, and it is particularly interesting from the fact that all 
the three forms were found both in the Maldives and Philippines 
in each case in the same habitat. According to the rules of 
nomenclature the species should be termed F. rubrum , the two 
varieties being var. stokesi and var. nutrix. The names of the 
type and its varieties exemplify the singularly unfortunate 
and inelastic character of these rules. The naming of a type- 
form among the above three forms is obviously undesirable. 
Further the form, originally described, merely represented an 
exceptional case of normal variability, probably brought about 
by environmental or habitative influences, the usual operative 
cause among corals 1 . 
The largest specimens of F. rubrum are characterised by 
having 24 equal septa fusing to one another by trabeculae in 
the centre of the corallum, forming a false columella. In de- 
velopment there are at first 6 septa, which subsequently join 
together. Additional septa are formed and an additional 6 fuse 
by trabeculae with the first cycle. The corallite at this stage is 
seldom more than 2 or 3 mm. along the long axis of its calicle. 
Development now proceeds more slowly, and further septa only 
commence to fuse in the calicle, when a length of 8 to 10 mm. 
is attained. The scar of either of the three varieties is usually 
in the stage with 12 septa fusing, showing additional reason why 
the size of the scar is not a specific character. 
It is during this pause in the development that the larger 
mesenteries commence to receive their generative organs. At 
first there is a mere slight thickening of the endoderm on the 
two sides of the mesenteries behind the contorted ends of their 
filaments. This nutritive endoderm is very granular, and cell 
divisions are not apparent. Small testicular acini appear in the 
structureless lamella between its two layers. These are at first 
isolated, but partially by growth and partially by the addition of 
1 Vide “Marine Crustaceans, I. On Varieties,” by L. A. Borradaile, Fauna and 
Geogr. Maldives and Laccadives , Camb. Univ. Press, vol. i., Pt. n., pp. 193-8 
(1902). 
