till' mantle . wliidi liangs downward on all sides so that it encloses between 

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

 mantle cavit>-. This cavity is largest posterioii}- where it contains the anus, 

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



CG.-i~.-^ 



.1/0 - 



/ Ft 



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 tul^e 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 ganglion b\' 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 

 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 h'om its primitive condition. The dorsal surface of the embryo is 



Fit;. 2. 



