MATERIAL FOR STUDY. 13 
in the water below at the same time. A young 
whirligig is shown in Fig. 16. Watch mode of 
breathing and of carrying air about. Observe also 
the manner of ‘‘feathering’’ the oars. Feed the 
beetle and larve on bits of meat or small in- 
sects. 
Leeches. ‘‘ Blood-suckers’’, as the boys call them, 
are harmless and interesting tenants of an aquarium. 
Watch some of these animals, noting especially the 
mode of movement by means of contracting longi- 
tudinal and circular muscles. They feed only occa- 
sionally, and can be set at liberty before they suffer 
forfood. At liberty they suck the blood from living 
animals. 
Crayfish. These may be bought alive in the mar- 
Fic. 18.—Side View of Crayfish. amv, antenna; 7, rostrum; cep, cephalic 
portion; ¢ho, thoracic portion of cephalothorax; a4, abdomen. 
kets. They may be kept in shallow water in aquaria 
and fed on bits of fish or meat. 
Tadpoles. These may be caught in ponds and 
brooks even late in the fall. Collect several sizes and 
keep them in a jar or jars. They feed on vegetable 
matter, eating chiefly the small green plants (confervz) 
which grow so rapidly in stagnant water exposed to 
sunlight. Select a particular individual and sketch his 
