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BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
Development of larva . — Segmentation of the fertilized ovum is complete and 
nearly regular (see fig. 2). A blastula in the shape of a biconvex lens is formed 
and in its interior or blastocoele the primitive endoderm cells (end) become visible. 
These increase by division forming free cells which almost fill the blastocoele and 
represent probably both the endoderm and mesoderm. Small cavities occur in 
Fig. 2. — Early Stages in the Development of the Cheilostomata. 
See text for description of the figures. 
A-G. Drawings illustrating the development of Bugula. (After Vigelius.) 
cent, central mass of cells; cor, corona; ect, ectoderm; end, endoderm; seg, segmentation 
cavity. 
H. Longitudinal section of the attached larva of Bugula. 
o, cells of corona; r, rudiment of the zooid in the form of a sac; s, basal plate of everted 
sucker; v, vestibule. 
I. Larva of Bugula plumosa, highly magnified. 
J. Sagittal section of Bugula (H-J after Barrois). 
cent, central tissue; cor, corona; disk, retractile disk; e, ectodermal groove; int. sac, internal 
sack ; p, pyriform organ ; pall, pallial groove. 
this mass of cells and form the primitive coelome by their union. Next the equa- 
torial region of the embryo becomes thickened and provided with cilia forming the 
corona (fig. 2, G. cor.). On the oral side of the corona the circular pallial 
groove arises. The sucker, a structure which afterwards serves to fix the larva, 
then develops as a sac-like invagination of the ectoderm or what later becomes the 
oral side of the ciliated ridge. On the oral side near the corona a second depression 
