1. Formed bodies, similar to the spheroids of the crayfish antennal gland, are present in urine removed from the frog nephron and from the insect Malpighian tubule by micropuncture.
2. The formed bodies contain digestive enzymes and appear to function in the digestion of materials accumulated by the cells of the proximal portions of these excretory organs.
3. These results indicate that some concepts regarding the process of urine formation in animals are in need of reappraisal. It is possible that in the crayfish and other animals with filtration kidneys only very small molecules are filtered. In the Malpighian tubule the secretory basis of urine formation may be more firmly established. However, whether or not organic materials enter the urine by passive diffusion may be in need of reinvestigation.