22 THE VOYAGE OF H.M.S. CHALLENGER. 



knob, of several sizes, disposed in regular series at the margin of the disk, and in two 

 circlets on its surface." 



Setting aside such characters in this definition as are common to many Actiniae, 

 and are therefore only of secondary value for differential diagnosis, the following points 

 remain : — (1) The stiffness and slight contractility of the body, (2) the knobbed nature of 

 the tentacles, (3) their distribution in several series. I attach special importance to the 

 second and third characters, but the third requires to be more clearly defined, for it often 

 happens in the Actinise that some of the tentacles have migrated inwards, far on to 

 the disk, and are separated by a broad interspace from the marginal tentacles ; Moseley 

 has not taken into account a characteristic in the position of the tentacles which dis- 

 tinguishes the Corallimorphidae from nearly all true Actinise, viz., that two tentacles, a 

 marginal and an intermediate, communicate with the same intraseptal space. The 

 intermediate tentacles thus acquire special value, as they have not merely been pushed by 

 growth from the margin towards the centre, but may be considered as new formations of 

 independent origin. They are therefore distinctly opposed to the marginal tentacles, 

 have no homology with anything in most other Hexactinise, and consequently deserve 

 the special designation of " accessory" tentacles. 



In considering the tentacles we must not forget their varying size, especially as it 

 reveals at the first glance the whole arrangement of the body of the Actinia. Of the 

 marginal tentacles six are the largest, and are distributed at equal distances, then follow 

 six more the next in size, which halve the interspaces between the first six, then twelve 

 which come in the interspaces between the first six and the second six, and so on. This 

 also holds good for the intermediate accessory tentacles, so that we can speak of tentacle 

 cycles of the first, second, and third orders which completely correspond to the cycles of 

 septa. The equalisation of the tentacles, which is elsewhere met with, has not made its 

 appearance, and the arrangement according to cycles, which must be regarded as a 

 primitive condition, still predominates. 



An equally primitive condition is shown in the distribution of the reproductive 

 elements over all the septa, in the indistinctness of the cesojihageal grooves on the 

 oesophagus, and in the slight differentiation of the muscular system in all parts of the 

 body. The transverse and the longitudinal muscles form a uniform, hardly even slightly 

 pleated layer on the septa, so that both the strong retractor and the parietobasilar muscle 

 are still wanting ; the muscular layers on the oral disk and the tentacles are smooth, and 

 there is not the least indication of a special circular muscle. All this explains the small 

 capacity for movement in our animal, which is, moreover, due to the nature of the 

 supporting substance, which by its toughness reminds us of cartilage, and is richly 

 developed in the septa, the oral disk, and the wall. 



The close relationship of the Corallimorphidee to Discosoma, which Moseley declared 

 probable, undeniably exists. Verrill was the first to point out (Proceedings Elliot Soc, 



