The fibula is reduced to a mere rod-like rudiment of the upper end.
5, Rudiment of reaf; d, dermatogen.
The study of Rhabdocoels (7) has led to the important discovery that the rudiment of the gonads and that of the pharynx are the first organs to appear, and that the alimentary sac arises independently of them.
As in other Gastropoda Anisopleura, this shell-sac may abnormally develop a plug of chitinous matter, but normally it flattens out and disappears, whilst the cap-like rudiment of the permanent shell is shed out from the dome-like surface of the visceral hump, in the centre of which the shell-sac existed for a brief period.
PrGabp l, Rudiment of the appendage of the praegenital somite which disappears.