the mantle, which hangs downward on all sides so that it encloses between 

 itself and the visceral mass and the foot, a ring-shaped cavity, the pallial or 

 mantle cavity. This cavity is largest posteriorly where it contains the anus, 

 pairs of gills, of nephridial openings , and of sexual openings. These structures 



CG - 



Mo . 



Fig. 1. 



are called collectively the "pallial complex." The visceral dome is covered by a 



saucer-shaped or conical shell which extends downward over the mantle and 



mantle chamber. The intestine is a straight tube which is connected with a 



large digestive gland. The 



nervous system consists of 



a cerebral ganglion in the 



head, a pedal ganglion in 



the foot, joined to the 



cerebral gangUon by a pair 



of ganglionated nerve cords , 



and a visceral ganglion in 



the body also united to 



the cerebral ganglion by a 



pair of nerve cords. 



The general body-form 

 -and arrangement of organs 



Ai 



• .;;.-.Si>'. 



Fig. 2. 







A^ 



of the unspecialized mollusc are for a short time partially realized in embryonic 

 Cephalopoda. The egg of the Cephalopoda contains a large amount of yolk 

 -and undergoes a discoidal cleavage, hence the form of the embryo is greatly 

 modified from its primitive condition. The dorsal surface of the embryo is 



