DEVELOPMENT OF SOME STARFISHES. 565 



Fig. 4. Section of stomach-wall of 8 daj-s larva through posterior enteroeoelic body, 



which is here shown as a thickening with slight outpouching of the 



stomach-wall. 

 Fig. 5. Section of 10 days larva in similar region, showing posterior enteroeoelic 



body with a distinct lumen, and now nearly separated off from wall of 



stomach. 



S.cav., buccal cavitj' ; Z.ew^c, left enterocoele; oes., cBsophagus ; p-swie.', posterior 

 enteroeoelic body; po.cil.hd., postoial ciliated band; posf.pr., posterior 

 backwardlj' growing process of enterocoele, which normally gives rise to the 

 posterior enterocoelo on either side; pr.cil.bd., preoral ciliated band ; rect., 

 opening of rectum ; r.entc, right enterocoele ; st., stomach ; sLw., stomach- 

 wall. 



Plate IT, 



CrihreUa oculata. 



Figs. 6-9. Diagrams illustrating mode of origin of perihremal pouch I./II. from 

 posterior coelom. 



In fig. 6 the tip of the dorsal horn which is destined to become peri- 

 hoemal pouch I./II. is bending leftward to lie between hydrocoele pouches 

 I. and II. In fig. 7 an opening has appeared between the axial sinus and 

 the dorsal horn of the posterior coelom. In fig. 8 the axial sinus is again 

 becoming closed otf from the dorsal horn of the posterior ecelom, but in 

 such a way as to leave the tip of the dorsal horn still for a time connected 

 with the axial sinus. In fig. 9 this tip, i. e, perihsemal pouch I./II., is 

 seen isolated both from the axial sinus and from the posterior coelom. 



Land II., the first and second hydrocoele pouches respectively. a.r.s., axial 

 sinus portion of anterior coelom ; d.li.'p.c, dorsal horn of posterior coelom ; 

 ph.I.jII., perihasmal pouch I./II. 



Fig. 10. Section along preoral lobe and through disc of a 20 days CrihreUa larva at 

 a stage when retraction of the preoral lobe is in active progress (outlines 

 drawn with camera lucida). The retractor muscle described in the text 

 is seen to cause a sharp pouching of the preoral coelom towards the disc 

 superficial to the hydrocoele ring. Had this portion of the hydrocoele 

 ring been absent through the hydrocoele being an open crescent, the con- 

 dition in Solaster or in Asterina and Asterias might well have resulted, 

 the preoral coelom becoming continuous with the axial sinus and with the 

 developing internal periha3mal sinus on the oral aspect of the disc, as in 

 Solaster. If completion of the hydrocoele ring supervened prior to the 

 disappearance of this continuity, the result might well be an enclosure of 

 the stalk-cavity by the hydrocoele such as occurs in Asterina, Asterias 

 ruhens, and Solaster endeca. 



div., pouch from preoral coelom caused by pull of the preoral lobe retractor 

 muscle (r.muso.) ; epic/.c, the epigastric coelom ; gut., the enteron or gut ; 

 hi/p.c, hypogastric coelom (larval posterior coelom) ; hi/.r., the hj'drocoele 

 ring (in neighbourhood of pouch III.) ; liy.r.' , the hj'drocoele ring (between 

 ■ pouches I. and V.) ; or.s., internal oral circular sinus (internal perihiemal 

 ring); phar.c, pharyngeal coelom; pod., developing sucker-feet; pr.c, 

 preoral ecelom; r.mnsc, retractor muscle of the preoral lobe. 



Solaster endeca. 



Fig. 11. Specimen in late metamorphosis, from oral side, showing origin of hydro- 

 coele pouch IX. from the (larval) dorsal end of the hydrocoele crescent 

 (see p. 561). Contrast with PI. i. fig. 13 of 1, in the lettering of 

 which, however, VIII. and IX. should be replaced by VII. and VIII. 

 respectively. 



