THE CARNIVOROUS SLUGS OF SOUTH AFRICA. 185 



runs forward towards the ventral group of ganglia. Just 

 before reaching these a pair of arteries is given oif to the 

 tentacular retractors (PI. XIII, figs. 52 and 54-57). In most 

 of the species these arteries unite with the common tenta- 

 cular retractors just behind the points where the latter divide ; 

 but in Apera dimidia they unite with the upper tentacular 

 retractors, and give oif small branches to the retractors of 

 the lower tentacles, which join the nerves from the sides of 

 the "nerve-collar" (fig. 54). Finally the aorta fuses with 

 the ventral group of ganglia. 



From this point radiate numerous short vessels to the 

 various parts of the central nervous system, etc., as well as 

 two longer arteries, namely, the buccal and pedal arteries. 



The buccal artery passes upwards and divides into two 

 branches, one running forwards and the other backwards. 

 In Apera dimidia the posterior branch is about twice as long 

 as the other (PL XVII, fig. 103) ; it runs back to the posterior 

 extremity of the odontophore, which it enters, and then bends 

 round the hind end of the odontophoral support (PI. XVIII, 

 fig. 122). The anterior branch runs forward and divides into 

 a pair of arteries which apply themselves to the sides of the 

 buccal mass, dividing again as they do so into anterior and 

 posterior vessels. In A. burnupi and A. sexangula the 

 buccal artery bi-anches in a similar manner, but owing to the 

 small size of the odontophore, the posterior branch is no 

 longer than the anterior branch (PI. XVII, fig. 110). In A. 

 gibbon si and A. parva, on the other hand, the posterior 

 branch is very long, and in the former species the right and 

 left anterior arteries do not branch from a sing-le median 

 vessel, but arise separately (PI. XIII, fig. 52). 



In Testacella the artery supplying the odontophore with 

 blood behaves differently, for, instead of running straight to 

 the hind end of the organ, it divides into lateral vessels which 

 pass through the sides of the sheath as shown in de Lacaze- 

 Duthier's admirable figui-es.^ On the other hand, in Nata- 

 lina quekettiana {M. & P.), this artery behaves in the 

 ' 'Arch. Zool. Expei-.' (2nd ser.), 1887, vol. v. pis. xxxv. xxxvi. 



