70 DEVELOPMENT OF THE STARFISH SOLASTEE BNDECA. 



PLATE V. Figs. 49-56. 



(Diagrams illustrating the moulding of the various cavities at different stages as seen 

 from the larval left or oral (figs. 49-53) and from the larval right or aboral (figs. 54-56) 

 sides. Magnification about 18 times. Colouring as on PI. IV.) 



Fig. 49. Diagram from left side of internal cavities in a larva about eight days old. 

 The three primary divisions of the archenteron are becoming separated, 

 the anterior being the largest. The posterior coelom is beginning to send 

 out dorsal and ventral horns. 



Fig. 50. Diagram from left side of internal cavities in larva about eleven days old. 

 The dorsal and ventral horns of the posterior coelom have extended con- 

 siderably, and the hydrocoele groove or bottom of the left lateral diverti- 

 culum of the anterior coelom now shows the outgrowth of the first five 

 radial pouches and partly conceals the enteron. The larval arms have also 

 appeared. 



Fig. 51. Diagram from left side of internal cavities in a larva about fifteen days old. 

 The horns of the posterior coelom have grown round still further. Peri- 

 hsemal diverticula (o.ph.c.) are coming off from the posterior coelom, while 

 that from the anterior coelom has already become separated. The ring- 

 canal of the hydrocoele is beginning to be nipped off from the left lateral 

 diverticulum. The preoral coelom is still large. 



Fig. 52. Diagram from oral (left larval) side of internal cavities in a specimen during 

 early fixation. The dorsal and ventral horns of the posterior coelom have 

 grown round so far as to compress between them the structures of the axial 

 complex. The perihsemal diverticula of the posterior coelom are beginning 

 to be nipped off. The stalk of the preoral coelom is almost obliterated. 

 The hydrocoele is represented as already forming a complete ring, and as 

 separated all round from the anterior coelom, but this is slightly in 

 advance of the ordinary course of development. Fusion is taking place 

 between the enteron and the oral body-wall in preparation for the 

 formation of the mouth. Pouch I of the hydrocoele is represented as 

 being cut away close to its origin. 



Fig. 53. Diagram from oral side of internal cavities in a young Starfish towards 

 end of metamorphosis. The mouth-opening (mth.) has formed. The 

 pharyngeal coelom ( p.ph.c.) is not yet a complete circle, but it opens into 

 the hypogastric coelom {pg.c.) in most of the interradii. The perihaemal 

 pouches (o.ph.c.) are taking on their characteristic form. The tip of the 

 (larval) dorsal horn of the posterior coelom is pushing in the wall of the 

 dorsal sac, where it lies against the axial sinus, thus helping to form the 

 genital pocket {g.r.). The internal oral circular sinus (i.ph.c.) is still a wide 



