084. SYDNEY J. HICKSON. 
charged to the exterior. That absorption of the calcareous 
skeleton does actually take place in the formation of the 
ampulle seems clear enough. In Errina labiata a very 
complicated process of absorption must occur as the ampulle, 
when they contain the ripe embryo, project on the surface 
of the branches. Moseley says: “The ampulle are, in this 
genus, conspicuous bodies, since they appear as hemisphe- 
rical projections from the surfaces of the branches of about 
the size of a mustard-seed. In vigorous specimens they are 
closely crowded together in masses on both sides of the branches 
and branchlets in various regions of the flabellum. The 
ampulla commence as small cavities in the surface layer of 
the ccenosteum of the branches, and gradually enlarging in 
accordance with the development of the ovum contained in 
each, project more and more until those containing mature or 
nearly mature planule appear as conspicuous projections above 
described. A hemispherical cavity excavated in the surface of 
coenosteum corresponds with each ripe ampulla, but the exca- 
vation is usually not deep enough to render the entire ampullar 
cavity spherical in form. . . . . Im accordance with the 
gradual expansion of the ampullar cavity, its outer wall, which 
is finely reticular in structure, becomes thinner and thinner 
until no doubt it at last breaks away entirely, allowing the 
escape of the imprisoned planula.” 
I have no very conclusive evidence to bring forward of the 
way in which this absorption is brought about, but I am inclined 
to believe that the work is done by certain large ectoderm 
cells—calycoclasts—that I have occasionally found in the sur- 
face of very young gonophores. It is quite possible that the 
calycoclasts are generally carried away during the process of 
decalcification. This would account for their paucity in thin 
sections of decalcified specimens. 
When the diameter of the young ovum is approximately as 
large as the canal in which it is formed, a diverticulum of one 
wall of the canal is pushed out and the ovum retreats into it. 
At first this diverticulum is open to the canal by a wide mouth, 
but the lips soon become pleated or pouched and the proximal 
