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 aU the other tissues are 

 removed. There are several kinds of Bath Sponge, but we shall 

 take the fine Turkey Sponge, Euspongia Offtcinalis 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, a number 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 ; and 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. Eobert 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 of the 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 will now turn our attention to the small cells which 

 have the cilia or lashes. Scattered all over the Sponge are little 



