DEVELOPMENT OF THE STAEFI8H SOLASTBR ENDEOA. 67 



PLATE IV. (cont.). 



opposite sides of the enteron. The sucker is fully exposed. In this 

 section and the last the heightened epiderm {n.r.) over part of the preoral 

 lobe (larval nervous system, p. 46) is indicated. 



Fig. 43. Oblique section through left side of body of larva just prior to attachment, 

 showing a considerable number of the hydroccelis and perihsemal pouches 

 as well as the tip of the ventral horn of the posterior coelom. The hydro- 

 coele groove is closed off from the left lateral diverticulum of the anterior 

 coelom to form a canal in the region of pouches III to V. 



Fig. 44. Vertical section through disc, sucker, leaf, etc. in the specimen illustrated 

 in PI. II. fig. 21. The section passes transversely across the nuchal groove 

 (n.) about halfway between the margin and the middle of the disc. The 

 epigastric coelom {ep.c.) is not yet completely separated from the axial 

 coelom, nor the latter from the preoral coelom. The dorsal and ventral 

 horns of the posterior coelom appear in the section as well as the two 

 corresponding horns into which the enteron is drawn at this stage (p. 38). 



Fig. 45. Ventral section across disc of specimen in early metamorphosis. The section 

 does not pass through the centre of the disc, but falls well towards 

 the margin on which rays VII to IX will be formed. The prominence 

 on the oral side, due to the preoral lobe, is not yet entirely lost. The 

 perihsemal pockets for interradii VII/VIII and VIII/IX are in process of 

 being budded off from the posterior coelom. 



Fig. 46. Vertical section across disc about halfway between centre and margin in a 

 specimen in middle stage of metamorphosis. The section passes across the 

 madreporic interradius, and is to be compared with fig. 44 as regards 

 general orientation. The epigastric coelom is now completely separated 

 from the axial coelom. The latter is dividing into two horns {i.ph.c.) 

 which are continued into the internal oral circular sinus. On the right 

 side of the sketch the ring-canal of the hydrocoele is cut at its junction 

 with the stone-canal, and on the left side between pouches VIII 

 and IX. 



Fig. 47. Typical vertical section across disc in metamorphosis some time prior to the 

 formation of the mouth. The enteron has expanded very markedly, and 

 shows a flattened area on the oral side, in the middle of which the mouth 

 will afterwards be formed. To the right the radial vessel of arm III 

 appears, while to the left there is the shorter radial vessel of arm VII. 



Fig. 48. Vertical section across half of disc of a specimen four and a half months old. 

 Mouth and anus have been present for a considerable time. The anal 

 opening does not appear in the section, but some of the commencing 



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