THE DEVELOPMENT OF ASTERINA GIBBOSA. 403 
Fics. 27—29.—Three sections of a larva slightly older than the preceding. 
Fig. 27 shows that on the left side the ccelom is divided into an anterior 
ceelom a, and a left posterior coclom Jpe. Fig. 28 shows that this division 
only extends about halfway to the ventral side. Fig. 29 shows that the 
separation of the ccelom from the archenteron commences venirally, since here 
the ceelom is shut off from the gut. ¢r. First trabecula. 
Fie. 30.—Section of a larva rather older than that shown in Figs, 27—29. 
le. Larval cesophagus. ¢r. Trabecule cords of cells spanning the left pos- 
terior celom. 
Fic. 31.—Sagittal section of larva about Stage B, to show the formation of 
the larval esophagus. It is clearly seen that this is a stomodzum which has 
not as yet joined the gut. 
Figs. 82—34.—Three sections of a larva younger than Stage C. The 
segmentation of the clom on the left side is complete; on the right side it 
has begun dorsally (Fig. 32). The left water-vascular rudiment or hydroccele 
(/hy.) has appeared as an outgrowth of the anterior ccelom, its lobes numbered 
asin Pl. 18. Fig. 32 shows Nos. 1 and 2; Fig. 33, No. 3; and Fig. 34, Nos. 
4 and 5. 
Fie. 35.—Section of a larva of Stage C. The first trace of the right hydro- 
cele (riy.) has appeared. 
Fig. 36.—Section of a slightly older larva than preceding. The development 
of the right hydroccele is more advanced. 
Fies. 37—41.—Five sections of a larva of Stage D, or slightly younger. 
In Fig. 37 we see a section of the pore-canal (pe.) and the origin of the rudi- 
ment of the oral celom (or.c.). In Fig. 38 the fully developed form of the 
right hydroceele (r/y.) is shown. In Figs. 39 and 40 we see the left posterior 
ceelom extending obliquely beneath the right posterior ccelom (7pe.); this is 
the right ventral horn (/'p'c’.) of the left posterior celom. In Fig. 41 we 
see it opening into the anterior ceelom. 
PLATE 20. 
‘The same remarks apply to this as to Plate 19, but- in addition it is to be 
remarked that the epithelium of the pore-canal and of the stone-canal is 
distinguished by a cross-striation. 
Figs. 42 and 43.—Two sections of a larva rather younger than Stage D. 
ste. Rudiment of the stone-canal. Fig. 42 shows the septum between the 
anterior ccelom and the left posterior ccelom broken down dorsally ; and Fig. 
43 shows that the septum between the anterior ccelom and the right posterior 
ccelom is still incomplete ventrally. 
Figs. 44—46.—Three sections of a larva of Stage D. Fig. 44 shows the 
opening of the pore-canal into anterior celom; Fig. 45, opening of the stone- 
canal into the same; aud Fig. 46, the opening of the stone-canal into the 
VOL. 38, PART 3.—NEW SER. DD 
