244 MORPHOLOGY OF INVERTEBRATE TYPES 



opens into the mantle cavity at the base of the gill. A ductless 

 branchial gland is inclosed in the core of each gill. The function 

 of these glands is not known. 



Excretory system and ccelome. The excretory system of 

 the squid stands in close relation to the circulatory system and 

 the ccelome or secondary body cavity. It consists of a bilobed 

 sac the nephridial sac and a urinary gland. The sac opens 

 into the mantle cavity by means of two nephridiopores situated 

 on small papillae, one on each side of the rectum. The intestine 

 passes through the nephridial sac and emerges from it as the 

 rectum. The two nephridial arms of the anterior vena cava and 

 the nephridial portions of the two posterior venae cavae are in- 

 closed in the lobes of the nephridial sac. Surrounding these 

 vessels and hiding them from view are the two urinary glands 

 which are therefore likewise inclosed in the nephridial sac. The 

 ccelome connects directly with the nephridial sac by means of 

 t\vo short canals. It is lined with ciliated peritoneum. The 

 systemic heart, the branchial hearts, the stomach, the stomach- 

 pouch, and the gonad are contained in the ccelome (visceral 

 sac). 



Nervous system and sense organs. The nervous system 

 is characterized by the great concentration of the paired ganglia 

 of the central nervous system and the high development of the 

 sense organs. Four pairs of ganglia enter into the formation 

 of the cesophageal ring. They are inclosed in the cephalic 

 cartilage or skull and are almost completely fused together. 

 Of these four pairs of ganglia the cerebral ganglia lie above the 

 cesophagus, the pleural ganglia form the sides of the ring, while 

 the pedal ganglia and the visceral ganglia are situated below the 

 oesophagus. The pedal ganglia lie in front of the visceral ganglia. 

 Two large optic ganglia are closely connected with the pleural 

 ganglia. Two large stellate ganglia are situated on the inner 

 surface of the mantle just behind the nuchal cartilage. They 

 are connected with the visceral ganglia and supply nerves to 

 the mantle. Several other ganglia are found in the head and 



