THE DEVELOPMENT OF ALCYONIUM DKHTATUM. 87 
(10) Later on tlie third day the stomodasum and month 
arise by the appearance of a rapidly deepening invagination 
of the oral surface, in the centre of the circle of tentacles. 
Yolky detritus is still present in the coelenteron. 
(11) On the fourth day the base of this invagination de- 
generates, and so the coelenteron communicates with the 
exterior. 
(12) While the mouth invagination is still in process of 
formation, the endodermic portion of the mesenteric filaments 
arises on the six ventral mesenteries by a proliferation of 
cells on the upper part of the free edge. 
(13) On the fifth day the ventral mesenteric filaments are 
completed by strap-like ectodermic downgrowths from the 
stomodasum over the endodermic thickening on each mesen- 
tery. 
(14) On the sixth day the dorsal mesenteric filaments arise. 
(15) The dorsal and ventral mesenteric filaments appear 
homogeneous in origin, though of diverse function. 
(16) On the seventh day the eight filaments reach about 
half way down the free edges of their respective mesen- 
teries. 
(17) Further development consists of elaboration of the 
organs already present. 
(18) At the end of the third week the first bud is formed, 
and the solitary polyp becomes a young colony by stolonal 
gemmation. 
(19) The young colonies were successfully fed in the labor- 
atory on larvae and adult individuals from colonies of Lepto- 
clinum and Botryllus. 
15. Literature. 
1. Bourne, G-. C. — “ The Calcareous Skeleton of the Antliozoa,” 
‘ Quart. Journ. Micr. Sci.,’ vol. 41, 1898-1899. 
2. Hickson, S. J. — “ Alcyonium,” ‘ L.M.B.C. Memoirs,’ No. v, 1901. 
3. “The Anatomy of Alcyonium digitatum,” ‘Quart. 
Journ. Micr. Sci.,’ vol. 37, new series, 1894-5. 
