CH. VII] SNAILS AND SLUGS 229 



discharge into the vagina; the fluid contains abundant 

 calcareous matter and is thought to contribute to the outer 

 covering of the eggs. The dart-sac is very muscular and 

 contains the dart or spiculum amoris. This extraordinary 

 weapon, which is flexible when within the sac but soon 

 becomes brittle after removal, consists of a slightly curved, 

 hollow, calcareous stem with four projecting and slightly 

 twisted longitudinal flanges placed at right angles to each 

 other; the stem and its flanges taper off to a fine point 

 anteriorly. The muscular walls of the sac push the dart, 

 with a slight screwing motion imparted by the flanges, into 

 the body of the mate prior to sexual union. Owing to 

 its slender attachment the dart frequently breaks off during 

 use, and is left in the body of the mate. It appears to act 

 as a sexual stimulant. A new dart is formed in about a 

 week by the lining of the sac. The exact shape of the 

 dart varies remarkably in the different species of Helix. 



The eggs are laid during July and August in moist 

 earth, under heaps of leaves and stones, and in similar 

 places. They are about a quarter of an inch in diameter and 

 enclosed in a tough calcareous shell containing a quantity 

 of albumen and a small ovum. All the eggs of a season 

 are not deposited simultaneously but in separate batches 

 of from 20 to 60, one act of impregnation is however 

 sufficient for the fertilisation of all 1 . 



Self-fertilisation is said to occur occasionally in the slug 

 Arion ater 2 and in the aquatic snail Limncea auricalaria' 3 . 



1 Gaskoin, Ann. Mag. Nat. Hist. (2) ix. 



2 Wotton, Journ. of Conch, vn. 1893. 



3 Braun, Nachr. Deutsch. Malak. Gcsell. xx. 



