582 JAMES F. GEMMILL 
A mesogloeal sheet only begins to form after the ectoderm 
and endoderm have come in contact. Accordingly it appears 
first at the oral end of the larva. Both layers seem to take 
part in its formation. 
Comparison with other Anemones as regards 
the Stages up to the end of gastrulation. 
Metridium dianthus.—Nuclear division and segmenta- 
tion go together from the first ; blastula with a hollow central 
cavity ; endoderm formed by invagination (Gemmuill, 9). 
MeMurrich, however, stated (15) that the endoderm is formed 
by delamination. Sagartia troglodytes.—As in Metri- 
dium. Adamsia palliata.—Cleavage begins after the 
second nuclear division; the preblastula is a wrinkled dise, 
becoming saucer-shaped, and then smooth and spherical or 
oval; the inner yolky ends of the cells separate off to form 
a central trophenchyme normally without nuclei ; gastrulation 
is by invagination (Gemmill, 9), and the trophenchyme passes 
through the inpushing endoderm into the archenteron. Faurot 
(7), however, stated that the endoderm is formed by delamina- 
tion. Urticina crassicornis.—Development is much the 
same as in Bolocera. Cleavage, however, begins when there 
are sixteen nuclei in the egg, and the trophenchyme nuclei 
are sparing or absent. ‘The crumpling and folding of the wall 
of the early blastula which I find to be very well marked in the 
eges of Urticina have not been described by Appelléf in his 
otherwise excellent account of the development of this species 
(1). Actinia bermudensis.—Harly stages not deter- 
mined; gastrulation by invagination (Cary, 5). Actinia 
equina.—Harly stages not determined ; endoderm formation 
by invagination according to Jourdan (12), but by immigra- 
tion or delamination according to Appellof (1), who states that 
the mouth opening is a secondary break-through.t Cerian- 
thus and an Actinian allied to A. equina.—HKndoderm 
formation by invagination (Kowalevsky, 18). 
Movements.—Cilia are acquired during the middle blastula 
1 My own observations (Millport, 1920) are entirely in favour of the 
open invagination method of endoderm formation in this species. 
