WOTTON : LIFE-HISTORY OF ARION ATER. 165 



attention of all these enemies, fortunate indeed is the Arion 

 who lives out the full term of its natural existence, which gener- 

 ally terminates at the end of the second year or early in the third. 



A great many slugs die soon after the exclusion of the eggs, 

 especially when a large number has been deposited, the effort 

 apparently being too much for their vitality. Oft times the 

 creature dies a seemingly painful death. Little blisters form on 

 the margin of the respiratory orifice, which gradually increase 

 in size until the aperture is completely closed, and the Arion 

 dies slowly from suffocation. A short time before death, the 

 shield is elevated into a hump by the air confined in the pul- 

 monary cavity. This sweUing, which is elastic to the touch, 

 gives the animal a somewhat ludicrous appearance. Death is 

 also caused by the attack of an internal parasite, the effect of 

 which has a very peculiar result. The superior tentacles, which 

 are partly exserted, thicken at the base, and the animal loses the 

 power of projecting or withdrawing them. It also becomes 

 costive; finally, the digestive organs are projected some distance 

 out of the mouth, the body becomes rigid, and death ensues in 

 two or three days. 



Arion ater is monoecious — that is, the sexes are combined 

 in the same individual ; therefore, each slug has the power of 

 producing eggs. It develops both spermatozoa and ova, but, 

 it has been asserted, not at the same time. It occurred to me 

 that, under these conditions, the Arion, when unable to find a 

 mate, possibly possessed the power of self-fertilization, and I 

 resolved to try and ascertain whether it did or not. 



I will now give the result of my investigations, by which I 

 discovered that they do possess this power. Out of one of the 

 batches of young slugs produced by the light Arion, I selected 

 three of the strongest and healthiest. These I placed each in a 

 separate box made specially for the purpose, thus completely 

 isolating them. The boxes were provided with glass fronts, 

 which commanded a full view of the interior, and so every 

 movement of the occupant could be noted. 



