REPORT ON THE ACTINIARIA. 120 



tentacles are mesodermal; the strong sphincter, which is also enclosed in the mesoderm, 

 lies close under the endoderm, and contracts the wall so strongly that the surface becomes 

 arranged in ridge-like, projecting folds. The tentacles only are different ; they are placed 

 in four alternating rows, are equal to one another in size, and are much longer and more 

 powerful than in Dysactis crassicornis, so that even when contracted they form slightly 

 curved horns 3 cm. long. The most striking point, however, is the wide, gaping opening 

 at the free end, from which one might give the animal the specific name tubuUfera. 

 This Actinia probably belongs to the genus Paractis, the smooth surface of the wall, the 

 mesodermal circular muscle, and the equality of size in the tentacles of the individual 

 rows being common to both. The two specimens of this Actinia before me are both 

 3 cm. high and 6 cm. broad at the pedal disk ; they become smaller towards the upper 

 end, the diameter of which only amounts to 2 "5 cm. 



The last Actinia to be considered belongs to the forms in which the tentacles have 

 iindergone retrograde formation, on account of which I have named it Liponemo, 

 m ultiporum. The only specimen of it was hardened in chromic acid and also greatly 

 injured, a combination most unfavourable for examination. The pedal disk and the lower 

 part of the wall were torn, the oesophagus forcibly protruded and also torn, so that the 

 oral disk was stretched and misplaced ; it formed the side walls of the body, and this led 

 me at first to take it for the wall and the wall for the pedal disk, till I discovered my 

 mistake in examining it histologically. 



The oral disk is devoid of freely moving tentacles, but has instead numerous, 

 small stomidia, roundish openings not measuring more than 2 mm. in diameter. The 

 tentacles in Liponema midtiporum have undergone retrograde formation to a greater 

 extent than in any other Actinia, as there are not the smallest remains of then- walls, 

 while in Polyopis these can still be recognised as thickened ridges surrounding the 

 openings (PI. XIV. fig. 7). 



Part of the stomidia, which number several hundreds, are arranged on the margin of 

 the oral disk in a repeatedly waved circle, the remainder lie at short distances from one 

 another on the oral disk, on which they are distributed nearly to the oral opening. After 

 dissecting a number of septa I became convinced that more than one stomidium 

 communicates with each radial chamber ; in fact, I believe that the marginal openings 

 must be considered principal stomidia, the others accessory stomidia. We therefore 

 have here the same conditions as in the Discosomidee and Corallimorphidse, if we 

 consider the tentacles to be replaced by the stomidia. The oral disk is covered with 

 numerous fine ridges which wind between the accessory stomidia and so have a very 

 sinuous course. The radial muscles are ectodermal and borne by fine supporting folds, 

 having the same constitution as in Cerianthus. I have also examined the circular muscular 

 system of the wall ; I found it thickly pleated in the whole upper region of the wall, 

 especially in the part adjoining the oral disk, where it formed a kind of sphincter. The 

 pleating ceases rather suddenly at the outer margin of the principal stomidia. The 



(ZOOL. CHALL. EXP. — PART XV. —1882.) P \'J 



