D, Embryo with lateral torsion and an endogastric shell.
Such cannulated cells are characteristic of the nephridia of many worms, and the organs thus formed in the embryo Limnaeus are embryonic nephridia.
The parasite effects a lodgment in the host either by invading it as a free-swimming planula, or, apparently, in other cases, as a spore-embryo which is captured and swallowed as food by the host.
The name expresses the most universal character of the class, the importance of which was first noticed by John Ray, namely, the presence of a pair of seed-leaves or cotyledons, in the plantlet or embryo contained in the seed.
Areas are found on the foot of the embryo Pulmonate Limax and on the yolk-sac (distended foot-surface) of the Cephalopod Loligo.