The British Guiana Museum. 231 
horn coral (Millepora) are made by minute beings, 
lower in organisation, similar to the little fresh-water 
polype (Hydra) found commonly in ponds, but differ- 
ent from it in habit since they live in colonies and secrete 
a skeleton of lime. These little beings, or, as they are 
technically called, zooids, are curiously modified to 
perform different functions : some only feed, others again 
only procure food and defend the colony; while the 
latter are gathered several together around each of the 
feeding-zooids. These hydra-like beings and the sea- 
anemones both take the form of a double-layered, 
cylindrical bag, one end of which is furnished with an 
aperture to the cavity within, and is surrounded with 
a circlet of feelers, or tentacles, for offensive and defensive 
purposes, while the other end fixes itself to rocks, etc. 
If this bag-like cavity be cut across, the hydra-forms are 
seen to have only a simple hollow space or stomach in 
the middle, while the sea-anemone has, besides, a series 
of folds or vertical divisions forming several chambers. 
The animals that form coral belong to one or other of 
these two closely-allied groups, the few hydra-like forms 
being classed as the Hydrozoa, and the numerous forms 
which are like the sea-anemones as the Anthozoa or 
Flower-like animals. 
Along the rest of the table is shewn a large collection, 
almost entirely of foreign shells, the arrangement of 
which will soon be revised and localities notified. As 
at present shown, the different kinds of shells are often 
mixed. In general terms, they consist of three kinds: 
(1.) The bivalve shells or shells of two pieces, techni- 
cally forms of the class Lamellibranchiata, so called on 
account of the form of the gills (branchiae) which are 
GG 2 
