414 DR F. A. BATHER. 



leads to the same conclusion — that the elliptical organs subserved nutrition. This 

 granted, let us consider how they did so. 



§ 228. A Pelmatozoon need not have any trace of a stem ; but every known 

 Echinoderm with a stem is a Pelmatozoon, and as such obtains its food "by a sub- 

 vective system of ciliated grooves." There is no reason to suppose that in this respect 

 Cothurnocystis was any exception. It has been shown that each of the elliptical 

 organs was in part a groove, and the view that the whole of the long U constituted a 

 ciliated subvective groove is confirmed by the presence of cover-plates arranged as in 

 all the most typical of Palaeozoic Pelmatozoa. 



§ 229. The actual opening in the thecal wall presented by each elliptical organ 

 consists of two parts : the Y-shaped incision in the groove of the long U, and the 

 wider circular hole in the short ci into which it leads. This is probably connected 

 with a difference of function, and the possible interpretations are many. 



Memories of the Eleutherozoan ambulacral system, on the one hand, and of the 

 Blastoid subvective system on the other, at first evoked the idea that the circular 

 opening of the short u gave passage to a tentacle. On the Eleutherozoan plan this 

 tentacle would have been a podium, that is to say, an extension from the water- 

 vascular system ; but, though it might have subserved sensation and respiration, it 

 certainly could not have had a locomotor function. Podia of this nature, combined 

 with a ciliated subvective system, were, I have maintained, present in Edrioaster ; 

 but in that genus their relations to the food-groove and to the skeleton were in any 

 case quite other than in Cothurnocystis. This interpretation, then, though possible, 

 does not commend itself. On the Pelmatozoan plan this tentacle may have been such 

 an uncalcified, grooved extension of the body-wall as Haeckel supposes to have existed 

 in several primitive Cystids, and particularly in their hypothetical ancestors. But, 

 considering the degree of calcification manifest in this genus, it seems probable 

 that any such extension would have been calcified as a normal brachiole, and in 

 that case the short u would represent the facet for the brachiole. There is, no 

 doubt, a superficial resemblance to the subvective system of Mesocystis, of Astero- 

 hlastus, and of the Blastoid type generally ; but in all those the convincing evidence 

 is the definite facet with its fulcral ridge (cf. text-fig. 56), and there is no trace of such 

 a structure in Cothurnocystis. 



§ 230. The interpretation which approves itself to me is that the long U was 

 floored with a ciliated groove, and that the short u surrounded a veritable opening by 

 which the food-stream from that groove descended into the gullet. The incomplete 

 calcification of the floor of the food-groove suggests that space was required for the 

 passage, not only of nerve-filaments leading to sensory-tentacles, but of an extension 

 from the water- vascular system, branching it may be into small lateral podia. When 

 in full swing, the cover-plates were open, the tentacles or podia were fully protruded, 

 and a stream of sea-water was driven down each of the fifteen or more grooves, and 

 diverted by the hood of the short u through the round mouth. Then some passing 



