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 ? 
Fig. 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. 
