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POPULAR SCIENCE REVIEW. 
The bodies grouped under this term by modern naturalists are 
thus summarily described by Professor Reay Greene : * — “ All 
are furnished with an alimentary canal, freely communicating 
with the general or somatic cavity. The substance of the body 
consists essentially of two separate layers, an outer, 6 ectoderm,’ 
and an inner, or fi endoderm.’ These two membranes, but es- 
pecially the former, are in general provided with cilia.” Another 
common characteristic is the presence of thread-cells, which are 
stinging organs. These, in a simple form, are easily seen when the 
tentacles of a common polyp (hydra) are squeezed in a compres- 
sorium, or live-box, and viewed with one-fourth or higher power. 
The more complicated and elegant forms found in sea ane- 
mones, which belong to the Coelenterata, are described and 
figured by Mr. Gosse in his 66 Devonshire Coast.” The Ccelen- 
terata have no proper blood-vessels, but the cilia cause currents 
of digested matter to flow to various parts. 
There are two leading groups of Coelenterata, Hydroza (polyps 
simple, or in colonies) and Actinozoa, of which the anemones 
may be taken as types. In the hydrozoa, the digestive cavity is 
not distinct from the general body cavity, and “ the reproductive 
organs are external.” In the Actinozoa the wall of the 
digestive sac is separated from that of the somatic cavity by an 
intervening space, subdivided into chambers by a series of 
vertical partitions, on the faces of which the reproductive 
organs are situated.” | 
Colonising polyps are well represented by the Sertularians, so 
common near sea-coasts, found adhering to large sea-weeds, 
shells, bits of rock, &c., thrown up by the tides. In these 
formations we have elegantly branching trees of a horny-looking 
substance, bearing numerous cells, in each of which a polyp 
lives. Each polyp catches its own prey, digests its own dinner, 
and leads its own life ; but all the polyps have a share in the 
general colonial life, and contribute to its growth and stability. 
Mr. Hinck’s admirable work, “ British Hydroid Zoophytes,” 
should be in the hands of all who visit the sea-side, or who wish 
to know the 66 fairy tales of science ” that are to be told concerning 
these exquisite and astonishing creatures. For the present it is 
enough to point to the general character of their organisation, 
and to the fact of their living in a colonial associated life. 
Amongst the compound polyps are the Alcyonaria, a common 
specimen of which is often seen on our coasts as a gristly- 
looking, whitish or yellow-brownish mass, with finger-like pro- 
jections, and popularly called “ Dead Men’s Toes ” \Alcyonium 
digitatum). If alive, and placed in salt water, this repulsive- 
looking object assumes an aspect of fascinating beauty ; star- 
shaped polyps protruding from numerous pores, and spreading 
* Manual of Coelenterates. t Greene, op. cit. 
