200 ZOOLOGY SECT, iv 



and so propelling the animal through the water. The combs are, 

 in fact, rows of immense cilia, fused at their proximal .ends : their 

 presence and mode of occurrence arranged in meridional comb- 

 ribs or swimming-plates are strictly characteristic of the class 1 

 and indeed give it its name. 



It will be seen at once that apart from all considerations of 

 internal structure Hormiphora presents a similar combination of 

 radial with bilateral symmetry as some Hydrozoa, such as Ctenaria 

 (Fig. 96, 1}, and as the majority of Actinozoa. The swimming-plates 

 are radially arranged, and mark the eight adradii, but the slit-like 

 mouth and the two tentacles indicate a very marked and character- 

 istic bilateral symmetry. A plane passing through the longitudinal 

 axis of the body, parallel with the long axis of the mouth, is called, as 

 in Actinozoa (see p. 176), the vertical plane : it includes two per-radii, 

 which are respectively dorsal and ventral. A plane at right angles 

 to this, passing through both tentacles, and including right and 

 left per-radii, is called the transverse plane. 



Enteric System. The mouth leads into a flattened tube (Fig. 

 146, std.),often called the stomach, but more correctly the gullet or 

 stomodceum. It reaches attout two-thirds of the way towards the 

 aboral pole, and its walls are produced internally into ridges (std. r.\ 

 which increase the area for the absorption of digested food. 

 Living prey is seized by the tentacles, ingested by the aid of the 

 mobile edges of the mouth and digested in the stomodseum, which 

 is thus physiologically, though not morphologically, a stomach. 

 The products of digestion make their way into the various parts 

 of the canal-system, presently to be described, and indigestible 

 matters are passed out at the mouth. 



Towards its upper or aboral end the stomodseum gradually 

 narrows and opens into a cavity called the infundibulum (inf.), 

 which probably answers to the stomach of an Actinozoon or a 

 medusa, and is flattened in a direction at right angles to the 

 stomodaeum i.e. in the transverse plane. From the infundibulum 

 three tubes are given off: one, the infundibular canal (inf. c.), passes 

 directly upwards, and, immediately beneath the aboral pole, divides 

 into four short branches, two of which open on the exterior by 

 minute apertures, the excretory pwes (Fig. 147, A, ex. p.). The two 

 other canals given off from the infundibulum are the per -radial 

 canals (per. c.): they pass directly outwards, in the transverse plane, 

 and each divides into two inter-radial canals (int. c.), which in their 

 turn divide each into two adradial canals (adr. c.). These succes- 

 sive bifurcations of the canal-system all take place in a horizontal 

 plane (Fig. 147, B), and each of the ultimate branches or adradial 

 canals opens into a meridional canal (mdr. c.), which extends up- 

 wards and downwards beneath the corresponding swimming-plate. 

 Furthermore, each per-radial canal gives off a stomodceal canal 

 (std. c.), which passes downwards, parallel to and in close contact 



