Xll INTRODUCTION. 



1. Tegumental' y System. The skin is sufficiently distinct. 

 After a few hours' maceration in fresh water {Sag. bellis), 

 the epithelial and pigmental cells are easily removed with 

 a hair-pencil, leaving the outer layer of muscular fibre hare. 

 If the specimen be immersed in spirit for a day or two 

 (A. dianthus), the integument may be separated in flakes, 

 which, under the microscope, are seen to be composed of a 

 multitude of short corrugated fibrillar set in no definite 

 direction, interspersed with clear granules, pigment grains, 

 and cnidae. 



An examination of the living animal (dianthus, bellis, 

 crassicornis, Hale. chrysantJiellum, Cor. viridis, &c.) shows 

 that the skin is composed of three elements, though these 

 cannot always be separated. A layer of epithelial ciliated 

 cells forms the first tunic : these are constantly in process 

 of being thrown off from the true skin, in the form of 

 mucus ; but in some cases (Phellia, Edwardsia) they 

 entangle foreign matters, and retain their cohesion as an 

 investment more or less dense, and more or less firmly 

 adherent to the skin. Below this is the true skin, of a 

 more granular character, and carrying, imbedded in its 

 thickness, a multitude of cnidse, whose discharging points 

 are directed outwards. Intimately connected with this 

 layer, but still lying sufficiently beneath it to be regarded 

 as a distinct stratum, are the pigment-cells, which impart 

 the colours to the animal. 



The tentacles of Aiptasia and Anihea (less conspicuously 

 also of S. bellis) are lined with a dense layer of cells, forming 

 to the naked eye a dark brown lining. Some peculiarities 

 of these cells I have detailed (at page 167, infra) : it is 

 probable that this layer may have some special function yet 

 unrecognised. 



2. Muscular System. In most species the muscular frame- 

 work of the body is beautifully distinct, and the tissue is 

 readily isolable. The column is a cylinder of muscular 

 tissue, consisting of two layers, the outer composed of 

 transverse, the inner of longitudinal, fibres. The trans- 

 verse fibres are the more strongly marked : they average 

 about "0001 inch in diameter, and are never striate. 



The cylinder which forms the column, is closed in most 

 species by two extremities, which are flat, like the top and 

 bottom of a tin canister: the former is the disk, the latter 

 the base. Each of these is but a continuation of the same 



