Fig. 2. Distribution of substance P-like labeling in the commissural ganglion (CoG) of the crab Cancer productus. (A) Within each CoG, substance P-like immunoreactivity is present in seven neuronal somata (three denoted by arrows) as well as in neuropilar processes (star) and a large club-shaped plexus (boxed). This plexus is located in the anterior medial quadrant of the ganglion and originates from a fascicle of small-diameter axons that project from the circumoesophageal connective (coc) connecting the supraoesophageal (SoG) and thoracic ganglia (TG) to the CoG. This micrograph is a brightest pixel projection of 24 optical sections taken at 2.0 µm intervals. (B) A higher magnification view of the plexus boxed in A. As can be seen from this micrograph, the plexus is composed of tightly aggregated, flocculent varicosities. The aggregated varicosities appear to cluster around unlabeled tubular structures, particularly in the posterior portion of the plexus. This micrograph is a brightest pixel projection of 37 optical sections taken at 1.0 µm intervals. (C) A projection of three optical sections taken at 1.0 µm intervals from the boxed region in B, showing aggregated substance P-immunopositive terminals enveloping several unlabeled tubular structures (indicated by asterisks). Scale bars, 200 µm in A, 75 µm in B and 25 µm in C.