3224. Pisces. 27 Color Photomicrographs. 1. Petromyzon, lamprey, region of gills t.s. 2. Petromyzon, lamprey, region of abdomen t.s. 3. Scyllium, dogfish, t.s. young in region of gills 4. Scyllium, t.s. young in region of spiral intestine 5. Fresh water