Filtration slits are formed by

The cells of inner epithelium of Bowman’s capsule are modified to podocytes. These podocytes have foot-like projections called pedicels which wrap around the capillaries leaving spaces in between called slit pores or filtration slits. These pores along with fenestrae in the blood capillaries allow the flow of filtrate into the Bowman's capsule from glomerulus.