418 EARLY DEVELOPMENT OF CRIBRELLA OCULATA. 



Figs. 53-57. A sagittal series through stage D. ( x 28.) (The selected sections are Nos. 20, 22. 30, 

 40, 42.) 



Figs. 58-62. A transverse series through stage C/D. (The selected sections are Nos. 5, 30, 49, 54, 56.) 

 ( x 28.) 



Figs. 63-70. A coronal series through stage D/E. ( x 28.) The selected sections are Nos. 26, 32. 36, 

 49, 58, 52, 67 and 71.) 



Figs. 71-76. A transverse series through stage D/E. ( x 28.) The Selected sections are Nos. 19, 30, 

 37, 43, 57, 66.) 



Plate IV. 



Figs. 77-78. Dextral and sinistral views, respectively, of stage E. (x28.) 



Figs. 79-87. A coronal series through stage E. ( x 28). (The selected sections are Nos. 54, 60, 64, 

 73, 83, 90, 100, 116, 129.) 



Figs. 88, 89. Dextral and sinistral (aboral and oral) views, respectively, of stage F. ( x 28.) 



Fig. 90. Anterior view of stage F. ( x 28.) 



Figs. 91, 92. Aboral and oral views of stage G. ( x 28.) 



Fig. 93. Anterior view (larval) of stage G. ( x 34.) 



Fig. 94. Another specimen of stage G, showing quadrifid pre-oral lobe. ( x 28.) 



Fig. 95. An enantiomorphic specimen, oral but right side. ( x 28.) Stage G/H. 



Plate V. 



Figs. 96-104. A selected series of coronal sections through stage F. ( x 57.) (The selected sections 

 are Nos. 48, 53, 56, 60, 64, 76, 85, 90, 97.) 



Figs. 105-106. Left and right views of stage F, seen as transparent objects, cleared with oil of cloves. 

 ( x 34). 



Figs. 107-111. Diagrams illustrating the suggested homologies and fates of the ccelomic elements in 

 Asteroiclea and Crinoidea. 1 = pre-oral coelom. la = central coelom. 2 = left lateral ccelom or hydrocoele. 

 2' = right lateral coelom. 3 = posterior coelom. The details of each coelomic element have been omitted, and 

 the figures are at most approximate diagrams. 



Fig. 107. Dorsal view of the asymmetric (sinistral) ancestor of Echinodermata. The mouth is on the 

 left side. The stage D/E of Cribrella, except for absence of mouth and anus, is closely similar to this stage ; 

 it is also represented by the larva of Antedon, which, however, has no mouth, and its hydrocoele is deflected 

 towards the ventral surface. This stage is slightly later than that shown in Diagram 3 (A). 



Fig. 108. The early axo-symmetric stage; the sedentary habit is sufficiently pronounced to reflect 

 itself in axo-symmetry ; the mouth has commenced its migration towards the posterior end ; the hydrocoele 

 commences to surround the oesophagus, the posterior coelom also commences to encircle the stomach. 

 N.B. — No attempt is made to indicate the 4/5 position of the stone-canal. 



Fig. 109. The ancestor of the Crinoidea ; the mouth is now terminal, the oesophagus is encircled by 

 the hydrocoele, the stomach by the posterior ccelom, which becomes the ' oral coelom ' ; the right lateral 

 ccelom, now the aboral coelom, is growing out into the stalk to form the chambered organ ; the pre-oral 

 coelom remains as the ' parietal canal.' It should be noted that the mesentery between posterior and right 

 lateral cceloms crosses diagonally, as has been indicated in Antedon (Bury) and Asterina (Ludwig). 



Fig. 110. The fully formed ' cystid' stage of Antedon. 



Fig. 111. The early asterid stage, set free at a stage intermediate between stages B and C (above). 

 The posterior coelom is here seen to form the hypogastric, and the right lateral becomes the epigastric 

 coelom. The pre-oral coelom remains, in part, as the axial sinus, in the mesentery of the hypogastric ccelom, 

 alongside of the stone-canal. 





