a, GENERAL REMARKS. 
in the radial corallites the directive septa are most frequently better developed, either stouter 
or broader, than the other primaries. In certain groups of species, however, the outer 
directive septum is more important than the inner; and in case only one septum is present 
it is invariably the outer directive. Apparently the number, but more particularly the 
relative importance, of the septa form characters of value for the classification of species. In 
several of the subdivisions now proposed the species were first associated together on general 
grounds, and without any regard to the condition of the septa ; and yet, in almost every case, 
the relative importance of the septa will be found nearly constant—e. g., Lepidocyathus and 
Trachylopora. Tn certain species there appear to be two types of radial corallites. In the 
usual more or less prominent one the septa are naturally least developed in the young buds 
near the apex, and there is a gradual increase in importance in older corallites until the 
normal condition is attained. It may be that the condition of the septa is subject to little 
variation whether the corallite be prominent or immersed, situated near the apex or near the 
base of the corallum. In certain species, however, some of the immersed corallites of the 
upper surface of the corallum have quite a different development of the septa to the 
prominent ones. Sometimes the septa in these immersed corallites are more numerous 
or better developed—a condition which might be attributed to age; but that this is not 
always the case is clear from the fact that such corallites often contain more septa than the 
axial corallites, or, on the other hand, may show an almost complete absence of septa. 
Similarly, prominent corallites on the under surface of prostrate or vasiform specimens may 
show a condition of the septa quite distinct from that characteristic of the upper surface. 
Whether in the case of the axial corallites the relative importance of the directive septa 
is usually associated with a variation in the size of the tentacles situated over them is not 
known. In Dana’s figures of the axial polyps of M. cribripora and M. aspera the tentacles 
are shown of equal length. In Agassiz’s ‘ Florida Reefs’ the polyps of M. cervicornis and 
M. prolifera are figured, and in both cases the tentacles are drawn alternately large and 
small, corresponding evidently to the broader primary and narrower secondary septa. This 
arrangement is in accordance with Lacaze-Duthiers’s figures of the embryo of Astroides. 
Mr. Saville-Kent informs me that in his experience of the Torres-Straits and Barrier-Reef 
species the tentacles of the axial polyps are always of equal length, even in species in which 
this does not hold good for the radial polyps. So far as I am aware, Dana does not anywhere 
state the wswal condition of the tentacles of the radial polyps in Madrepora in the living 
specimens which came under his notice. There seems reason to suppose that they were 
generally of equal size, from the fact that he figures them as such without comment in the 
case of M. aspera. With regard to M. prostrata he calls special attention to the fact that 
one of the tentacles is much longer than the others, and that this is situated over the outer 
directive septum, which is itself broader and stouter than the remaining septa. That this 
arrangement was not usual in his experience will be rendered clear from the following 
quotation :—“ Among the species of Madrepora there are some in which one of the tentacles 
of the polyps is long and flexible. This was observed in a cespitose species (M. prostrata) 
haying thin labellate calicles ; but whether it belongs or not to all the horizontally-growing 
