THE CARNIVOROUS SLUGS OF SOUTH AFRICA. 181 



THE VASCULAR SYSTEM. 



The Heart and Pulmonary Veins. — The g-eiius Apera is 

 opisthopneuniic, the greater part of the respiratory tissue 

 being behind the heart. Unlike Dandebarclia, the auricle 

 has moved round with the pulmonary veins so as to lie 

 obliquely behind and to the right of the ventricle (PI. IX, 

 figs. 27-31), but it has not rotated so far as in Testacella. 

 The pulmonary veins form a complicated network, variable in 

 its structure ; but it is generally possible to distinguish three 

 main vessels converging towards the auricle, namely, the right 

 anterior pulmonary vein, from the corner of the mantle-cavity 

 to the right of the pericardium ; the right posterior pulmonary 

 vein, from the region between the pericardium and the anus ; 

 and the left posterior pulmonary vein, from the part of the 

 mantle-cavity behind the kidney. Owing to the absence of 

 the respiratory tissue from the left anterior corner of the 

 mantle-cavity there is no left anterior pulmonar}" vein. 



The walls of the auricle are very thin (PI. XI, fig. 85), Ijut 

 those of the ventricle are extremely thick and muscular 

 (fig. 34). The cardiac muscle-fibres are arranged in bundles 

 passing in various directions, and leaving spaces between them 

 which communicate freely with the central cavity of the ven- 

 tricle (PL XXII, fig. 140). The muscles are thus well supplied 

 with blood without the intervention of any cardiac arteries. 



The Arterial System. — The distribution of the principal 

 arteries is shown in PI. IX, figs. 27-29 and 31. The single 

 aorta leaves the posterior end of the ventricle, passes through 

 the diaphragm, and then bends abruptly to the right and 

 curves downwards, so that it comes to lie on the right side of 

 the liver. In Apera gibbonsi, A. parva, A. burnupi, 

 and A. sexangula the so-called posterior aorta branches off 

 to the left within 3 or 4 mm. of the diaphragm. This vessel 

 passes forwards on the right side of the left division of the 

 liver, keeping to the left side of the intestine. It divides into 

 two or three branches supplying the left division of the 

 liver, but the most anterior branch first passes through the 



