120 
ME. H. N. MOSELEY ON THE 
Millepora, in finely ground sections of the corallum, the tortuous canals become filled 
with opaque debris, and show out, when the section is viewed by transmitted light, 
dark on a light ground. In a species of Millepora obtained at Zamboangan the corallum 
was of this nature. The appearance presented by a thin section of its corallum is shown 
in Plate 2. fig. 7. In Millepora alcicornis and in the Tahitian species the canal-systems 
and trabeculae of calcareous matter seem to form equally complex interpenetrating 
meshworks. The canal-systems present in the coralla of the species of Milleporidce are 
perfectly characteristic structures, and distinguish the coralla formed by these Hydroids 
most clearly from all other recent coralla whatever*. They of course correspond to, and 
in the recent state contain, the ramifications of the soft parts of the hydrophyton. The 
canals form regular branching systems with main trunks which give off numerous 
branches, from which arise secondary branches, and from these again smaller ramifi- 
cations. The wdiole canal-system is connected together by a freely anastomosing 
meshwork of smaller vessels, and communicates freely by numerous offsets with the 
cavities of the calicles. In Plate 3. fig. 12 part of one of these canal-systems is shown, 
being there drawn from a decalcified specimen, and thus representing the soft tissues 
which in the recent state occupied corresponding calcareous canals. In Plate 2. fig. 6 
a secondary branch of one of the canals is seen to communicate with a calicular cavity, 
C'. The course of the smaller vessels being tortuous, only short lengths of them are 
exposed in the remainder of this section. Similar secondary branches are seen in 
vertical section in Plate 2. fig. 5, B, B. 
Where a Millepora encrusts foreign bodies, the investing film of corallum formed is 
usually extremely thin. At Bermuda, Millepora alcicornis is frequently found encrust- 
ing glass bottles thrown into the harbours. The film of corallum can, in such specimens, 
easily be detached in flakes from the glass, and does not measure more than from ^ 
to ^ of a millimetre in thickness. In the same manner at Bermuda the dead fans of 
a Gorgonia are found entirely encrusted with a thin film of Millepora , so thin that the 
fenestrations of the horny meshwork of the Gorgonia are not obliterated. Such thin 
encrusting films, if obtained in the living condition, would, no doubt, be excellently 
adapted for the study of the soft parts of Millepora , since they are thin enough to 
transmit a considerable amount of light. When dead and dry they show extremely 
well the ramifications of the canal-systems and their connexions with the calicles. In 
such films the calicles, larger and smaller, are fully developed, though necessarily very 
shallow ; and it is evident that such a thin film of corallum is all that is absolutely 
necessary for the existence of the Millepora. and, in fact, in all Milleporce it is such a 
thin film only which is actually living, covering the surface of the corallum. In a 
Millepora forming tubercular or ramified masses a superposition of a series of such 
films takes place and constitutes the coral mass. 
In the films encrusting bottles the under surface in contact with the glass is perfectly 
* Note, June 1877. — Excepting the coralla of the Stylasteridse, since found by me to he also Hydroids and 
not Anthozoans (Proc. E. Soc. no. 172, 1876, p. 93). 
