MOLLUSC A 



135 



batches, with an interval of about a week or ten days between 

 each batch, whilst the other laid 477 in four batches. These 

 eggs hatch about sixty days after being deposited, the little 

 slugs burying themselves in the ground for four or five days 

 without feeding, and then emerging nearly double their original 

 size. They are not full grown until the second year, and 

 usually live two seasons only. 



B. 



cluster pfecgs. 



FIG. 87. Arion ater. 



A, Slug extended, showing the open respiratory aperture in the mantle ; 

 B, contracted. 



Slugs generally spend the day lurking under 

 stones or logs, or buried in the earth, coming out 

 at night to feed. They do great damage to plants. 



Like snails, they can secrete a copious flow of mucus from 

 the foot, and besides using this in making the trail along 

 which they glide, many slugs use it, at times, to form a 

 rope, by means of which they can lower themselves from a 

 height and then climb back again. When about to descend 

 in this way, the slug attaches the mucus to some surface 

 and then drops, the mucous string remaining attached to 

 the end of its tail. When re-ascending, it turns round and 

 climbs up, collecting the mucus in a mass near the tail. 1 

 (Compare with the mucous thread formed by Limnaea, see 



p. 110.) 



1 Wallis, Nature, October 1890. 



