2 
characters, and yet united closely together by a fundamental 
similarity, and at the same time separated from all other animals. 
Let us first take a Bath Sponge and examine it closely. What we 
know as the Sponge is simply the skeleton of the animal, a delicate 
elastic network which still presents a faithful model of the general 
form and structure of the whole, after all the other tissues are 
removed. There are several kinds of Bath Sponge, but we shall 
take the fine Turkey Sponge, EHuspongia Officinalis of which there 
are several well marked varieties, differing greatly in form. Some 
are cup-shaped masses with thick walls, or more or less globular 
clumps; others flat plates and others encrusting patches. The 
colour of the outside is usually brown, varying in shade within ; 
it is generally paler, but in one variety a rusty red colour. A thin 
skin covers the whole surface of the sponge rising tent-like about 
the projecting ends of the chief fibres of the skeleton. These 
projecting ends can readily be seen with a lens on an unused 
skeleton of a Bath Sponge. In various places, irregularly dis- 
tributed, the skin is perforated by circular holes known as oscula, 
which I shall call ‘little mouths ’’ which can be opened or closed. 
They are the openings of wide tubes which come from the inside 
of the sponge, being formed by the repeated joining of many smaller 
tubes. I will call these tubes the outward channels, they are very 
visible in our sponge. Over the surface of the Sponge, where there 
are no little mouths, anumber of ridges are seen descending, like 
the spokes of a wheel, away from the centre, but branching as they 
go, and joined at their sides by cross ridges which make an irregular 
network with meshes; aud in these meshes may be seen with a lens 
a number of minute openings which we will call ‘‘ pores,” making the 
meshes look rather like a sieve. These pores open into a 
space beneath the skin, and from this space the inward channels 
spread into the substance of the Sponge. Thus the Sponge 
consists of a fleshy mass, supported by a network of elastic 
fibres, invested with a skin and traversed by two sets of 
canals; the outward, each opening by a single little mouth to the 
exterior, and the inward, which communicate with the exterior 
by these sieve-like groups of holes. Dr. Robert Grant, of Edinburgh, 
about 1827, was the first to discover a constant flow of water with 
floating particles of food into the pores, and inward channels, and 
out ofthe outward channels, and little mouths. He rightly con- 
jectured that this stream of water constantly flowing in and out, 
must be due to ciliary action, but he was unable to find the 
cilia; they were subsequently found by Dobie, Bowerbank, and 
Carter. We wiil now turn our attention to the small cells which 
have the cilia or lashes. Scattered all over the Sponge are little 
chambers about ,)) in. in diameter, which are lined with micros- 
