MUSSELS AND SNAILS. 163 
movements of the foot. Examine the trail of mucus 
left as the animal advances. 
Do you find the place from which this mucus comes? 
Do you find a head? a neck? 
What organs of sense do you find? Describe their 
position. 
How does the slug feed ? Has it a shell ? a mantle? 
On which side of the body is the breathing orifice ? 
How often does the slug breathe ? 
How often do you breathe ? 
Is there any relation between rapidity of breathing 
and rapidity of movement ? 
Do you call the slug’s body warm or cold ? 
Fic. 128.—A Slug. 
Does the rate of breathing have anything to do with 
the snail’s temperature ? 
Write resemblances and differences for slug and fresh- 
water mussel. 
Sketch the slug as you see him. 
Pond-snails. These animals are found in almost 
all ponds, crawling on dead leaves or aquatic plants. 
They may be easily kept in a jar of water for class- 
study. Get some pond-snails and keep them in a jar 
of fresh water. Watch all their movements. 
Write resemblances and differences for snail and 
slug. Note all points mentioned in regard to slug and 
mussel. 
