226 SNAILS AND SLUGS [CH. VII 



vibrations of the cilia of the epithelial lining. The nerve 

 supply is derived from the cerebral ganglia. 



Reproduction 1 . All the pulmonate gastropods are 

 hermaphrodite, and, as is usually the case when both 

 male and female organs are present in the same in- 

 dividual, possess complicated reproductive systems. In- 

 asmuch as the details of structure differ in various species 

 we shall here confine ourselves to the arrangements found 

 in Helix pomatia. The hermaphrodite gland or ovotestis 

 situated in the upper coils of the digestive gland, is the 

 seat of origin both of ova and spermatozoa ; the latter are 

 the first to mature, whence each individual functions first 

 as male, and is termed " protandric." The ovi-sperm-duct 

 (hermaphrodite duct) receives the spermatozoa or ova, as 

 the case may be, from the gland and by means of its 

 ciliated lining wafts them on to the confluence of the 

 duct of the albumen gland. At the breeding season this 

 gland increases in size and secretes a viscid albuminous 

 substance with which the ova become surrounded. From 

 the point of entry of the albumen duct onwards a separate 

 course is provided for the ova and spermatozoa respectively. 

 The spermatozoa pass, probably by their own vibratile 

 movements, along the narrow and granulated portion of 

 the " common duct " ; the ova are urged by ciliary action 

 down the wide and much folded section of the same duct. 

 Thus the "common duct" though structurally one is 

 functionally two tubes, a well-marked longitudinal con- 

 striction virtually separating the two internal channels. 



1 Garnault, C. R. Acad. Sci. Paris, cvi.; Baudelot, Ann. Sci. Nat. 

 Z.ool. (4) xix. 1863 ; Ashford, Journ, of Conch, iv. 1883. 



