Kidney of a pigeon (HE): cortical collecting tubules
The collecting tubules in the kidney of birds are located in the cortex and in the medulla. The cortical collecting tubules (tubuli colligentes corticales) have a pale, cuboidal epithelium and are therefore hard to distinguish from the distal convoluted tubules. The cells of the collecting tubules however carry apically mucous granules which stain dark on HE staining and PAS-positive on PAS staining. The lateral membranes of these cells are clearer visible.