Formation of the entoderm, attach- 
ment of the larva and development of 
the hydranth. 
18 Section of blastula with entoder- 
mal cells just beginning to bud 
off from posterior end. 
19 Section of posterior end of blas- 
tula with a few entodermal cells 
given off. 
20 Blastula with more entodermal 
cells migrating into blasto- 
coele. 
21 Blastula with blastocoele full of 
entodermal cells. 
22 Planula with entodermal cells be- 
coming re-arranged. 
23 A few ectodermal cells with 
higher magnification, showing 
an interstitial cell and nemato- 
cyst. 
24 Cross section of planula a little 
older than one shown in longi- 
tudinal section in figure 22. 
25 Larva at the time it settles down. 
26-32 Attached larva with hydranth 
bud in various stages of de- 
velopment. 
