Fig. 3. General organization and morphology of peptidergic epithelial endocrine cells in the midgut proper (MG) of Cancer crabs. Regardless of species (Cancer productus shown), immunolabel (anti-substance P shown) or location within the midgut proper (posteriormost portion of the midgut shown), the gross organization and morphology of the intrinsic peptidergic endocrine cells was similar. All cells possessed an enlarged basal region and extended a short beaded projection apically toward the midgut lumen. This organization is shown in a low-magnification view of the flattened midgut in A and in a high-magnification view of two immunolabeled cells in B. (A) A brightest pixel projection of 61 optical sections collected at 2.1-µm intervals taken at the midgut/hindgut transition (MHT); the boundary of each region is delineated. Note that no immunolabeling is present in the hindgut (HG). In this image, faint autofluorescence can be seen in the muscle fibers overlying both the MG and HG. (B) A brightest pixel projection of nine optical sections collected at 1.95-µm intervals showing two labeled endocrine cells at high magnification. Note that both immunopositive cells appear to span the entire epithelium, abutting both the midgut lumen and the hemocoel. Scale bars, 200 µm (A) and 25 µm (B).