254 MR. G. C. ROBSON ON THE 



than the auricle. Paired auriculo-ventricular valves of a simple 

 nature were found ; but apparently there is no aortic valve. 

 The course of the aorta was not followed, but its anterior branch 

 was found passing into the pharynx in the usual position ; 

 before doing which, it gives off several branches which con- 

 tribute to the cerebral vascular system referred to above. The 

 pulmonary vein (text-fig. 3) is very large. On its left-hand 

 side and particularly towards the anterior end of the pulmonary 

 cavity, it sends out several large branches which become very 

 much concentrated anteriorly. On the left-hand side there were 

 no particularly large vessels. In z l the pulmonary vein lies close 

 to the ureter — on an average 5 mm. from it. In the last respect 

 z differed from z v being much further away from the ureter. 

 The latter condition is seen in Archachatina bicarinata (Deshayes 

 (1821)) and also apparently in Limicolaria. The anterior con- 

 centration of large secondary vessels is seen in Achatina chryso- 

 leuca (Pilsbry (1904)) and in Arch, bicarinata. 



(3) Renal System. 



The kidney measures 58 X 11-12 mm. in z 1 and 42 X 9-10 mm. 

 in z.. Anteriorly it narrows off slightly to an obtuse point. 

 Posteriorly it exhibits a curious diagonal groove on its under 

 surface which separates off a sort of posterior lobe. This occurs 

 in both z and z 2 ; but it is doubtful whether it is of systematic 

 value, though it was absent from both specimens of var. fulgurata. 

 Another interesting feature is the presence of a sort of "heel" 

 projecting from the posterior end of the kidney. In both forms 

 this was disposed in prolongation of the main axis of the organ. 



(4) Nervous System. (Text-fig. 4.) 



General. — In the adult the central nervous system is covered 

 over by a dense layer of connective tissue which involves the 

 main ganglia and roots. This layer, which has been commented 

 upon by previous authors (Nabias (1894)), is exceedingly difficult 

 to dissect away even in young forms, while in most adults it 

 appears to have complete histological union with the surface 

 of the ganglia. In young forms it is less extensively developed, 

 less closely applied to the ganglia and more hyaline. The growth 

 of this sheath involves the anterior aorta and its cerebral 

 branches. It is hoped that a future work may be devoted to the 

 study of this sheath. This much may, however, be stated that, 

 whatever functions it may or may not have acquired in the 

 course of its intimate association with the surface layer of the 

 ganglia, it has certainly developed a great importance as pro- 

 viding additional holdfasts for the muscles of the head and 

 anterior part of the body. For example, the rhinophorial 

 retractors appear to be partly dependent on the postero-lateral 

 extension of this sheath. Interesting analogies are suggested 

 by this structure, particularly on the subject of its function as a 



