THE DEVELOPMENT OF OPHIOTHKIX FllAGILIS. 591 



Asteroidea, from which the right posterior coelom, called by 

 him the epig-astric coelom, arises as does the true right hydro- 

 coele, termed by him the central coelom. This tallies fairl}^ 

 well with Ophiura brevis, where the anterior evagination 

 divides into right and left anterior cocloras, and from the right 

 anteinor coelom Grave infers that the right posterior coelom (the 

 epigastric) is subsequently derived. In Cribrella oculata 

 the posterior evagination, as in Ophiura brevis, gives 

 rise solely to the left posterior coelom (hypogastric coelom). 

 The difference between the two is that in Cribrella oculata 

 the left hydroccele originates from the anterior rudiment, 

 whereas in Ophiura brevis it originates from the posterior 

 vesicle. This irreconcilable difference between these two 

 authors prevents us placing as much stress on the points of 

 agreement between them as we should otherwise feel bound 

 to do. When Ave recollect that Mastermau's results would 

 fall at once into line with what is known of the development 

 of other Asteroidea, if we make the assumption that the 

 supposed independent origin of the left posterior coelom from 

 the gut is founded on a mistaken observation, we shall, I 

 think, be justified in provisionally assuming that this is the 

 case. All that is known of the development of the coelom in 

 the classes of Echinoderms, apart from these two papers, can 

 be subsumed under the formula that, in all cases, the coelom 

 arises as a single bilobed evagination from the apex of the 

 archenteron. In the single Crinoid whose development is 

 known (viz. Antedon rosacea) the whole archenteron is 

 bodily ti-ansformed into the coelom, which then divides into 

 anterior and posterior portions, whilst from the anterior 

 portion the definitive gut subsequently arises as a pair of 

 out-growths. This late appearance of the gut is rendered 

 possible by the fact that it is functionless in the embryo. 

 In Holothuroidea the single out-growth also divides first 

 into anterior and posterior portions, and whilst the anterior 

 subsequently divides into anterior coelom and left hydroccele, 

 the posterior portion divides into right and left halves. The 

 right hydroccele is not developed. In Asteroidea (Bipinnaria), 



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