60 DEVELOPMENT OF THE STAEFISH SOL ASTER ENDBCA. 



PLATE II. Figs. 15-23. 

 (For lettering see pp. 55-56,) 



Fig. 15. Gastrula beginning to elongate, the blastopore being still widely open (p. 14). 

 (X40.)^ 



Fig. 16. Anterior end of cone bending to larval ventral side (p. 14). (x40.) 



Fig. 17. Young larva from right side showing the three larval arms, the position of 

 the sucker, and the hydroporic opening (p. 14). (x45.) 



Fig. 18. Older larva from right side at a stage just prior to commencement of flexion 

 and torsion of the preoral lobe (p. 16). (x40.) 



Fig. 19. Still older larva from left side. The preoral lobe is beginning to undergo its 

 change of position (p. 16). Several pairs of ambulacral ossicles have now 

 appeared, and these are shown as if in a cleared specimen (p. 41). The 

 larval arms are represented as being drawn close together (p. 15). The line 

 on the body indicates the direction of the muscular fibrillee referred to on 

 pp. 16, 47. The hydroporic pit seems larger than it should be, owing to 

 slight shrinkage in the (preserved) specimens from which figs. 18 and 19 

 were drawn. 



Fig. 20. Larva from left side, towards end of free-swimming stage. The preoral lobe 

 is much more sharply flexed on the body, which is now almost disc-like in 

 shape. Six pairs of ambulacral ossicles are present, (x 40.) 



Fig. 21 . Sketch of a larva which had recently attached itself by means of the sucker to 

 a small duck-weed. A section of this specimen, showing plant, sucker, etc., 

 is given in PL IV. fig. 44. The preoral lobe, which is seen in shadow, has 

 not yet undergone its full flexion and torsion. The edge of the disc is 

 slightly everted at one part and shows between it and the preoral lobe two 

 or three blunt swellings due to the hydrocoele pouches. The long groove 

 on the disc running towards the siicker is the nuchal notch or groove 

 (p. 22). (X 40.) 



Fig. 22. Specimen detached after about three days' fixation and seen from oral side. 

 The preoral lobe is now completely bent against the oral (left larval) 

 surface, the remains of the anterior arm being towards the middle of this 

 surface (p. 19). The sucker and the other two arms are nearer the 

 margin. Six of the radial pouches of the hydrocoele appear externally and 

 a rudiment of the seventh. ( X 40.) 



Fig. 23. Specimens detached after about six days' fixation and viewed from oral side. 

 Five of the radial pouches of the hydrocoele now shov,- swellings for the 

 sucker-feet. Compare with fig. 22. The preoral lobe has now almost 

 entirely disappeared. (x40.) 



This series is continued in figs. 13 and 14 on PI. I. 



