224 MORPHOLOGY OF INVERTEBRATE TYPES 



the large liver which opens into the stomach near its pyloric 

 end. 



Excretory system and body cavity. Li max possesses a 

 primary and a secondary body cavity. The former forms the 

 system of lacunae and blood sinuses and is devoid of its own epi- 

 thelial lining. The secondary body cavity or ccelome is reduced 

 to the space within the pericard and the lumen of the hermaph- 

 roditic gland. It has its own endothelial lining. The excre- 

 tory system consists of a single nephridium situated under the 

 shield in contact with the pericard. A ciliated funnel or nephros- 

 toma leads from the pericard into the glandular portion of the 

 nephridium, which is usually known under the name of kidney. 

 The ureter is a long, curved duct beginning at the posterior end 

 of the glandular portion and terminating in a nephridiopore in 

 the mantle cavity near the pneumostoma. 



Circulatory and respiratory systems. Limax has an open 

 circulatory system in which the central organ is represented by 

 the heart, while the connection between arteries and veins is 

 established through a system of lacunae and sinuses. The heart 

 is inclosed in the pericardium. It consists of a single ventricle and 

 a single auricle; the latter condition is due to the fact that the 

 animal has a single lung and consequently a single pulmonary 

 vein. In the normal position the auricle is in front of the ven- 

 tricle. The latter leads into a large aorta which soon divides 

 into a cephalic artery (called also aorta cephalica) and visceral 

 artery (called also aorta visceralis). The cephalic artery on 

 reaching the region of the pharynx gives off arteries to the ten- 

 tacles and then divides into a single buccal artery, and a single 

 recurrent pedal artery. The system of veins consists of numerous 

 short branches which open into two longitudinal lateral veins. 

 These form a renal sinus around the nephridium. Pulmonary 

 arteries leading from the sinus to the lung ramify into numerous 

 branches which give rise to equally numerous branches of the pul- 

 monary vein. The latter conveys the oxidized blood to the heart. 

 The blood is practically colorless and contains amcebocytes. 



