256 MR. G. C. ROBSON ON THE 



fused) on the right. In both specimens a grouping of the pedal 

 nerves into two tiers, one above the other, could be made out. 

 The upper tier consists of five roots, one anterior three median 

 (usually fused) and one posterior. Certain of the lower tier 

 roots are separate in origin but enclosed together for the first 

 2-3 mm. of their length in common sheaths of connective tissue. 

 The arrangement of these differs from side to side and in 

 individuals. In z„ there were seventeen roots on each side. 



Pallial and Visceral Nerves. — In neither example can it be 

 asserted that any nerve arises from the pallial centres. The 

 latter (as defined by the position of the cerebral-pallial connective) 

 is clearly marked off posteriorly from its neighbour and no 

 pallial root arises from it on either side. Pallial nerves arise, 

 however, from the posterior ganglion mass (viscero-abdominal). 

 We can only conclude that fusion of ganglia has gone so far that 

 the slight external divisions are not reflected internally. On the 

 right there is only one pallial nerve, on the left three. There 

 are three main abdominal and visceral nerves arising from the 

 posterior end of the complex. Z L and z o agree in these particulars. 



Cerebral Nerves. — From the cerebral ganglia there arise on 

 each side nine roots in z v eight in z„. These consist of three 

 large labial and pharyngeal nerves, two rhinophorial, optic, 

 buccal connectives, and two (one in z ) of uncertain distribution. 

 There is a certain amount of unimportant difference in the 

 position and distribution of the nerves between z and z 2 . The 

 buccal commissure is symmetrical and the ganglia closely fused. 

 On each side six pharyngeal nerves originate from these ganglia, 

 the origin of which is asymmetrical. 



The optic nerve is exceedingly slender and arises a little 

 posterior to the rhinophorial nerve. It enters the sheath of the 

 rhinophore above the latter nerve. In z the base of the rhino- 

 phore is innervated by a separate nerve arising just anteriorly 

 to the first mentioned rhinophorial nerve. Amaudrut (1886) 

 refers the innervation of the base of the rhinophores in Ackatina 

 panthera to a nerve arising from the anterior lobe. There is in 

 C. zebra no distinction into three distinct lobes as Amaudrut 

 described for his species, though traces of a fairly distinct lobe 

 corresponding to Amaudrut's " lobe de sensibilite " could be seen 

 in z 2 . Again, there is no fine branch of the rhinophorial nerve as 

 there is in A. panthera. 



(5) Reproductive System. 

 Neither specimen dissected was apparently in a state of 

 reproductive activity. The gonad which is situated in the 2-3 

 whorl, is succeeded by a slender duct which is straight for 

 about 6 mm. and then becomes stouter and more convoluted. 

 In the third whorl this passes into the spermoviduct. The male 

 portion of this, as in the Helicidee, forms a sort of gutter incom- 

 pletely covered by two more or less overlapping ridges. The 

 duets of the numerous prostatic follicles open into the bottom of 



