NUTRITION PROPER. 



341 



mals are the most highly organized among mollusca. 

 All the organs contributive to digestion, such as salivary 

 glands, liver, and perhaps pancreas, are found. 



Fig. 226. — Diagram of digestive system of a squid : eg, cephalic ganglion ; 

 (eg, oesophageal ganglion ; ce, oesophagus ; st, stomach siphon ; mg, 

 mantle ganglion ; vg, visceral ganglion ; H, heart ; G, gills. 



ECHINODERMS. 



In the echinus, or sea chestnut, we have perhaps the 

 most elaborate jaw structure to be found in the whole 

 animal kingdom — viz., the so-called " lantern of Aris- 



FlG. 227. — Jaws of a squid : 

 up, upper jaw ; /, lower jaw. 



Fig. 228. — The masticating appa- 

 ratus of an echinus. 



totle " (Fig. 228). This consists of five three-sided hol- 

 low prismatic pieces surrounding the oesophagus and 

 fitted together so as to make a somewhat conical whole. 

 Through each prismatic piece there runs, as through a 



