5°4 
CCELENTERA TES. 
may chance to come within reach. It is interesting to note that a Palythoa 
closely related to the Japanese form occurs in the Adriatic, and is also attached to 
sponges, scarcely a single specimen of the sponge in question being found without 
its polyp guest. The larvae hatched from the eggs of the Palythoa evidently 
perish unless they meet with one of these sponges; but the manner in which they 
find and recognise their particular host is quite unknown. Other species of 
Palythoa found on the American coast settle on the shells inhabited by hermit- 
crabs, covering the shell as an uninterrupted mass several lines thick, and the 
individual polyps rising to about an equal height above 
the general mass. The shell becomes disintegrated beneath 
this cover, and the polyp-stock then remains as the only 
covering to the crab. In this case there is mutual 
advantage, for the crab is covered and protected by the 
polyp-stock, while the polyp profits by its wanderings and 
enjoys constant change of water and new fields for food. 
An extraordinary form, very nearly allied to Zoantharia, 
has been described under the name of Polyparium 
ambulans, and is found in the strait dividing the island 
of Mindanao from that of Billiton. It consists of a colony 
three inches long and six wide, flattened from above down¬ 
ward, and therefore more or less ribbon - like; and the 
anterior cannot be distinguished from the posterior end. 
The upper surface of the colony is covered with peculiar 
polyps shaped like chimneys, the base being much wider 
than the top, which carries a round aperture. Each polyp 
is extremely minute, and has no tentacles. They stand 
in irregular transverse rows of from five to eight, differing 
in age and therefore in size; the lower side, on which the 
The small dried-up polyps are colony rests, being beset with protuberant suckers. These 
seen adhering in groups to, ™ .. . , , . ,. , 
the branching sponge. also differ much m size, but stand m regular rows divided 
by furrows, and serve for attaching the colony, and also 
enable it to creep. The colony can even be seen slowly climbing up and down small 
stones. The polyps have no septa in the digestive cavity, the inner side being quite 
smooth; and the lower end of each is not closed, but communicates with a large 
cavity running along the whole colony, and divided at regular intervals by partitions. 
From the foregoing observations it will be seen that in the soft 
division of the Hexactinia, or six-rayed anemones, there are botli 
single individuals and colonies of individuals joined together to form stocks; and 
there is also the same diversity in the skeleton-producing division—the corals 
proper, where we have both single individuals and stocks. Whereas however, in 
the soft division, the simple individuals are the more numerous and the colonies 
comparatively rare, among the corals the opposite is the case, the colony-forming 
types presenting almost innumerable varieties. This is not difficult to understand, 
since the soft anemones cannot well form complicated colonies, whereas the skeleton¬ 
forming polyps, by combining their skeletons, can build complicated structures, in 
order to raise themselves into more advantageous positions. We have first, then, 
Palythoa axinellce (somewhat 
less than nat. size). 
True Corals. 
