126 



third militate against both theories. But when we take into account that 

 in no instance, in the existing Echinodermata, where ovarian pores occur, 

 are they at the same time oral orifices, the balance seems to be in favor 

 of my view. This is all I desire to say upon the subject at present. 

 Although I now firmly believe that the valvular orifice in the Cystidea, 

 the larger lateral aperture of the Blastoidea, and the so-called proboscis 

 of the palaeozoic Crinoids are all oro-anal in function, yet I shall not main- 

 tain that view obstinately against good reason shown to the contrary. 



Corrections and additions. 



According to Prof J. Miiller's observations, it appears that in the 

 existing Crinoid, Antedon Europaeiis^ there is no annular canal around 

 the mouth. In the interior of the body there is a soft spongy substance, 

 which is full of small cavities that connect with each other through 

 numerous slender canals. This substance forms a pillar, the base of 

 which rests upon the bottom of the internal cavity of the cup, whilst the 

 summit touches the inner surface of the ventral intesjument, on one side 

 of the mouth. Miiller says it forms a sort of a spindle, around which 

 ^he intestine is wound. The ambulacral canals all terminate in this 

 spongy spindle.* The upper part of the spindle, therefore, towards which 

 all the canals converge, and in which they all terminate, must be regarded 

 as the centre of the ambulacral canal system. If I have understood him 

 rightly, the canals radiate, not from the mouth, but from the spindle. 

 The mouth is situated not in the spindle but on one side of it, and it can- 

 not, therefore, be the centre of the ambulacral canal system. He makes 

 no mention whatever of a circular canal around the mouth. The struc- 

 ture would be similar to that shown in fig. 50, ante p. 92, where the 

 shaded central space C, from which the canals radiate, may represent the 

 upper end of the spindle of A. Europceus and mv the mouth. 



It may be that I have not interpreted Miiller's description correctly, or 

 that he may have been mistaken. If it be as I understand it, then the 

 oft cited rule, that the mouth is the ambulacral centre in aJV^ of 

 the existing Echinodermata, must undergo an important alteration. 

 The word " all " must be struck out. Before such a change, how- 

 ever, can be made, we must have the details of the structure and con- 



'f * Ueber denJBau des Pentacrinus caput 31adusse, p. 58. He says.^— " "Wo die Tentakelrinne 

 Yom Arm. auf die S'cheibe ubergeht bleibt der Canal ULter der Tentakelrinne und gelangt 

 mit diesen zum Mund, in dem er weiter wird und zwischen Perisom und Bauch — 

 holenhaut verlauft. Am Munde senkt er sich in eine den Hohlen ein, "welche zahlreich 

 4icspongio3e miltlere Masse den Scheibe durchziehen, Alle 5 Canale munden in diese ein " 



