There are two types of respiration :

1. Direct respiration : In this type the atmospheric oxygen directly reaches all the cells of the body .e.g., protozoans, flat worms, coelentrates, insects etc.

2. Indirect respiration : It is the respiration in which oxygen first combines with blood in respiratory organs and then blood transports the oxygen to all the cells of the body e.g. earthworm, frog, human being etc.