CARADOCIAN CYSTIDEA FROM GIRVAN. 413 



a corresponding Intake. If, with such a creature as Dendrocystis in our minds, we 

 seek for structures that might be regarded as brachioles, we find only the tag and 

 tono-ue. But these are solid processes and lead to no mouth-opening ; nor indeed is 

 it consonant with the pelmatozoic habit to imagine an intake so close to the vent. 

 Trochocystis, with its thecal frame and plated integument, next suggests a search for 

 some opening through the marginals ; but our knowledge of these elements in 

 Cothurnocystis, thanks to the abundant material, is so complete that the absence of 

 any such opening is incontrovertible. A few imaginative but erratic writers have 

 suggested that nutriment may, in one or two genera, have been taken up by the stem. 

 If this ever were the case (which I do not believe), it certainly was not so in 

 Cothurnocystis with its thin stem of solid columnals. 



§ 226. We are forced, finally, to inquire whether the very peculiar organs in the 

 foot-half of the theca may not furnish the required intake. There is no doubt that 

 they do, and they have therefore been described under the heading Subvective System 

 (§§ 195, 218). But it took me a very long time to realise this. A fragment submitted 

 to me in January 1899 by Mrs Gray was returned with the note that it was probably 

 part of the anal face of a Pleurocystis on which the stem had been impressed, thus 

 simulating an ambulacrum. The structure was better displayed in the first fairly 

 complete specimen sent to me, G45 (C. Elizae, PI. III. fig. 31), yet for some years 

 it reminded me of nothing so much as the ambulacral area of an Echinoid, Next came 

 a fragment of C. curvata, and I thought I had to do with some extraordinary 

 pectinirhomb. Fortunately, I held my peace and said nothing. Then at last, in March 

 1911, Mrs Gray sent the whole of her material, and it became possible to draw up a 

 complete description, with each statement proved by verifiable evidence. 



§ 227. Accepting the bare facts of that description, let us discuss their meaning. 

 Since the elliptical organs of a single individual vary in nothing but size, they must 

 all have had the same function. The functions served by openings through the thecal 

 wall of an Echinoderm are nutrition, aeration, excretion, and emission of gonads. Of 

 these functions, excretion (using the term in a wide sense) was in this case served by 

 the anus at the other end of the theca. Aeration or respiration may be effected 

 through the integument itself when thinly plated as here, or through the anus, or by 

 extensions of the water-vascular system often connected with the subvective system, 

 or even by the mere rush of the food-stream through the gut ; in short, there is no 

 absolute necessity for gills, hydrospires, or special openings in the theca. The emission 

 of gonads may take place through any of the normal openings in the test, or through 

 temporary openings made for the purpose. Nutrition, then, is the one function that, 

 except in truly parasitic animals such as are not known among Echinoderma, seems to 

 demand a definite opening. It is true that in some Echinoderms the same opening 

 serves as both mouth and vent; but the anus of Cothurnocystis cannot have served 

 as a mouth on either pelmatozoic or eleutherozoic lines — for either microphagy or 

 megalophagy, as Prof W. J. Sollas might have put it. Thus this line of argument 



