handles: anatomy of acavus. 109 



of the penis, to a common point, and are all inserted on the columella. 

 The retractor of the buccal mass is closely attached to the tentacular 

 and labial retractors of the left side ; it passes through the nerve- 

 ring, under the oesophagus, and then divides into three strips ; these 

 are inserted on the ventral and lateral borders of the buccal mass. 

 The retractor muscle of the right ocular tentacle passes between the 

 penis and vagina. The retractor of the penis is terminal, and is 

 attached to the left side of the body-wall. 



The pedal gland is exactly comparable to that of Helix. It opens 

 in the usual position below the mouth, and extends back for about 

 two -thirds tbe length of the foot. 



Nervous system. — The cerebral ganglia {e.g.) arc large and close 

 together ; they are united together by a very broad commissure, and, 

 with the pleural and pedal ganglia, form a well-marked circuni- 

 cesophageal nerve-collar. The usual nerves are given off from the 

 cerebral ganglia to the anterior portion of the head, branches being 

 distributed to the tentacles, lips, etc. A pair of buccal nerves arise 

 from the anterior border, and are connected with two buccal ganglia, 

 situated ventro-laterally on the oesophagus near its junction with the 

 buccal mass ; they are united by a short commissure which runs 

 underneath the oesophagus. From these ganglia several nerves arise, 

 and are distributed, some to the buccal mass, others to the oesophagus, 

 and a fine branch accompanies each salivary duct, passing backwards 

 through the nerve-ring and innervating the salivary glands. Nerves 

 are given off from the pedal and pleural ganglia to the foot and body- 

 wall. A large posterior visceral nerve (v.n.) arises from the pleuro- 

 visceral mass ; it shortly gives origin to a nerve which runs along the 

 dilated portion of the hermaphrodite duct, and is distributed to that 

 structure and to the alimentary canal. The main division of the 

 visceral nerve bifurcates at the posterior end of the body, one branch 

 going to the heart and kidney, the other being distributed to the 

 convoluted portion of the hermaphrodite duct and to the albumen 

 gland. 



Reproductive organs. — The genitalia of Acavus Iwmastomus and 

 A. Skinner i have been accurately figured ' by Semper, 1 though his 

 description is somewhat meagre. All the species of Acavus are 

 furnished with almost identically similar reproductive organs as far 

 as the external characters go ; there is, however, a slight difference 

 observable between the groups represented by A. hcemastomus and 

 A. Waltoni respectively. (PI. IX, Tigs. 1 and 10.) 



In the former group the penis (p.) has very much the same calibre 

 throughout, though there is a gradual tapering off towards either end. 

 In the A. Waltoni group the anterior vestibular portion of the penis 

 becomes greatly elongated and constricted, it is thin-walled, and often 

 slightly coiled upon itself. This condition is not so perceptible in 

 A. Poleii (Fig. 11) as in A. Waltoni, though it is perfectly distinct, 



1 Op. cit. , pi. xii, figs. 7, 9, 10. 



