88 Introduction to Animal Morphology. 



hydranth, and may be clavate, cylindrical, or long- and 

 ribbon-like (Sarsia strangulata). 



No form exhibits adelo- or phanero-codonic gono- 

 phores indifferently, but each has its specific gono- 

 phore. The umbrella-like bell, in free forms, is con- 

 tractile (except in Clavatella, &c.), and by it the zooid 

 swims; hence it is called a nectocalyx. Dicoryne, 

 however, moves by cilia, not by a contractile bell. 

 The tissues making up this bell are: ist. A layer of 

 tesselated epithelium on its surface. 2nd. Loose 

 connective tissue, either homogeneous or with fine 

 fibres, containing neither collagen nor mucin, but 

 sometimes with stellate corpuscles. When homo- 

 geneous, it is described as being epidermal in origin, 

 and the fibres, &r., are considered ingrowths from the 

 deeper connective layer. This makes the chief mass 

 of the bell, but so little solid matter exists in these 

 masses of " animated sea water," that each 100 grains, 

 when dried, usually contains 2.50 grains of residuum, 

 and from 10 kilogrammes of an allied form, only 30 

 grammes of solid matter were extracted. 3rd. Smooth, 

 rarely monilated muscle fibres (?) in the velum and 

 lining of the bell-cavity. In a few forms the sub- 

 muscular connective tissue develops into a cartilage- 

 like (Fig. 12, E, c.r.} ring, below the circular canal, 

 parallel to the codonostome, and receiving the nerve 

 ring; or radial rib-like cartilage rods, equalling in 

 number the lithocysts, may lie in the outer surface of the 

 bell (some Geryonidae), or as a rod-like axis in the stiff 

 tentacles (some Trachynemida?, &c.) The gastro- 

 vascular canals may be below, or imbedded in, the 

 connective tissue of the bell. 



The marginal tentacles are usually simple, often 



