Their contraction causes the proboscis to be invaginated into its cavity (fig.
The invaginated layer is the enteric cell-layer or endoderm; the outer cell-layer is the dermic cell-layer or ectoderm.
B, invaginated head of a Cysticercus before the formation of the suckers; X 25.
Then follows the phenomenon of gastrulation, by which onehalf of the blastula is invaginated into the other, so as to obliterate the segmentation cavity.
The tion of liquid between the gonads themselves are extremely outer and the invaginated simple arborescent glands which cells.
The primitive shell-sac or shell-gland is well marked at this stage, and the pharynx is seen as a new ingrowth (the stomodaeum), about to fuse with and open into the primitively invaginated arch-enteron (fig.
B, A section through the same; a, the invaginated proboscis; b, proboscis sheath; c, beginning of the neck; d, lemniscus.
The invaginated cells (derived from the division of the four big cells) form the endoderm or arch-enteron; the outer cells are the ectoderm.
C, invaginated head of Cysticercus cellulosae, showing the bent neck and receptacle r; X 30.
Kowalevsky or a bug is invaginated into the yolk at the head end, the portion of (1871 and 1887) on the embryology of the water-beetle Hydrophilus the blastoderm necessarily pushed in with it forming the amnion.