66 DEVELOPMENT OF THE STAEFISH SOLASTEE ENDECA. 



PLATE IV. Figs. 36-48. 



(Illustrative sections of specimens in larval stages and in metamorphosis, drawn 

 with camera lucida to magnification of 25 times. The various cavities are coloured 

 as follows : — The posterior coelom and its derivatives are red and the enteron brown. 

 The preoral and axial coelom s are coloured yellow, as also are the hydroporic canal 

 and the internal oral circular sinus. The right lateral diverticulum of the anterior 

 ccelom (epigastric coelom) is shown in green, and the hydrocoele and dorsal sac in blue. 

 The dull ground-colour is space filled by mesoderm.) 



Fig. 36. Frontal section through larva about 8 days old. The blastopore is still open 

 and the middle chamber or enteron still communicates with the anterior 

 and posterior cceloms. The right and left lateral diverticula of the anterior 

 ccelom are beginning to grow backwards over the enteron. 



Fig. 37. Section similar to the last, but not perfectly frontal, through a slightly older 

 specimen. The enteron now appears as a distinct region, not simply as a 

 neck between the anterior and posterior coeloms. 



Fig. 38. Frontal section through slightly older specimen. The anterior and posterior 

 cceloms are completely separated from the enteron and the blastopore is 

 closed. 



Fig. 39. Transverse section of larva about middle of free-swimming stage. The 

 section passes through the hydropore, the ventral side of the larva being 

 uppermost. Both horns of the posterior coelom appear in the section, as 

 well as the dorsal sac and the first radial pouch of the hydrocoele. 



Fig. 40. Transverse section through middle of body of larva at stage slightly later than 

 that shown in fig. 38. The dorsal and ventral horns of the posterior ccelom, 

 as well as the right and left lateral diverticula of the anterior coelom, and 

 the enteron appear in the section. The right lateral diverticulum in this 

 example is very large. 



Fig. 41. Sagittal but not quite median section through a larva in the later free- 

 swimming stage. The preoral and axial sinus regions of the anterior 

 coelom are beginning to be marked out. Some of the perihasmal pockets 

 (o.ph.c.) are separated from the posterior coelom. The ventral horn of 

 this coelom is cut along a great part of its length. There is a statolith 

 within the posterior ccelom (p. 46). 



Fig. 42. Sagittal section through larva in still later free-swimming stage. Flexion of 

 the preoral lobe has begun, and accordingly while this lobe is cut in its 

 sagittal plane, the body of the larva is cut rather in the future oral- 

 aboral plane, the aboral (right larval) side being underneath. This 

 explains the position in the section of the right lateral diverticulum 

 (epigastric ccelom) as well as the fact that the posterior cffilom is cut on 



