Histochemical distribution of peroxidase in ascidians with special reference to the endostyle and the branchial sac.

The histochemical distribution of peroxidase was studied in 10 species of ascidians. In the endostyle, strong peroxidase activity was found in zone 7 in Ciona intestinalis, Ascidia zara, Ascidia sydneiensis samea, Cnemidocarpa areolata, Styela clava, and Pyrura vittata. The activity in zone 7 was weak in Styela plicata and Halocynthia hilgendorfi. Pyura michaelseni and Halocynthia roretzi showed only faint activity in zone 7, but showed strong activity in zone 9 and in the transitional zone, respectively. Pyura vittata exhibited peroxidase activity in zone 5 as well as in zone 7. Zone 8 was negative for peroxidase, but the cilia of zone 8 cells were distinctly stained for peroxidase in Ciona intestinalis and Cnemidocarpa areolata. These results show that wide species differences exist in the distribution of peroxidase in the ascidian endostyle. Peroxidase activity was also detected in the branchial sac, although here again wide species differences were noted in terms of peroxidase-positive sites. Peroxidase activity was also found in the postpharyngeal alimentary canal, but not in the tunic.