410 DR ARTHUR T. MASTERMAN ON THE 



The latter is unpaired, and he makes the following remark : — " In most Echinoderms 

 the posterior enterocoeles originate as paired structures ; and if the statements of Bury 

 and MacBride are correct, that the left posterior enterocoele of the larva forms the 

 hypogastric cavity of the adult, and the right posterior enteroccele goes to form the 

 epigastric ccelom, then, according to this, the large ventral pouch, which I regard as the 

 fused right and left posterior enterocoeles, really represents the left only, because it 

 takes no part in the formation of the epigastric body-cavity of the adult ophiurid, but, 

 with the left, does pass directly into the hypogastric" (p. 88). 



Further he remarks, "As to the origin of this structure" (the epigastric enteroccele) 

 " I have no direct observations to give, but certain facts have led me to believe that 

 it is formed from the right anterior enterocoele .... Against such an interpretation as 

 the above there is the fact that in no other case has the epigastric enteroccele been 

 observed to take its origin from the right anterior pouch" (p. 90). 



I must add that Grave's figures, so far as they go, carry out these assertions ; and 

 it is much to be hoped that he will be able to give a more exhaustive account of these 

 points. 



Crinoidea. 



If we pass to the Crinoids we notice at once that Cribrella has this in common with 

 Antedon, as described by Bury * and Seeliger,! that the ccelom arises by separate 

 anterior and posterior rudiments. It is well known that the posterior ccelom in 

 Antedon divides into right and left parts, which form aboral (epigastric) and oral 

 (hypogastric) cceloms respectively. This disagreement with Cribrella can only be 

 reconciled in one of two ways. Firstly, we may assume that the hypogastric and 

 epigastric cceloms of the starfish are respectively homologous with the oral and aboral 

 cceloms of the crinoid, as has been done by most zoologists, in which case, in the light 

 of the present work, we cannot allow that the posterior ccelom of Cribrella is the same 

 as the posterior ccelom of Antedon, the former being 3 -I- 3' or left and right opisthocceles, 

 whereas the latter would be 3 + 3' together and 2' (the right lateral ccelom or right 

 mesomere). This seems a peculiar view to take, but we may recollect that the anterior 

 ccelom of Antedon is 1 -f 2 or parietal canal (pre-oral ccelom) and hydroccele, hence it is 

 quite a different organ from the anterior ccelom of Cribrella under any view, for it has 

 no right element at all. Again, unless we make this assumption, we must acknowledge 

 that Antedon has no representative whatever of the right lateral ccelom. Whichever 

 way we look at the matter, the anterior ccelom of Antedon is asymmetric (formed 

 of a median and a sinistral element), therefore there is no inherent improbability in 

 the posterior ccelom being equally asymmetric, and consisting of a median posterior 

 and a dextral element. Lastly, the ccelomic development in Holothuroidea shows 

 that the combined origin of contiguous ccelomic elements is an actual fact. 



* Phil. Trans. Roy. Soc. Lond., vol. clxxix., 1888. 

 t Sbeliger, 0., Zool. Jahrb., Abth. Anat., 4, Bd. 6. 



