THE SUBGENUS PERSICARGAS (IXODOIDEA: ARGASIDAE: ARGAS). 17. A NEUROHEMAL ORGAN IN A. (P.) ARBOREUS KAISER, HOOGSTRAAL, AND KOHLS

A paraesophageal neurohemal organ is described in the adult Argas (Persicargas) arboreus Kaiser, Hoogstraal, and Kohls. The tissue of this organ, studied by light and electron microscopy, consists of several large neuronal cell bodies and nerve axons, both containing neurosecretory vesicles, and numerous glial cells. The cellular structure of this organ suggests a structural homology to the corpora cardiaca of insects and to neurohemal endocrine organs in other arachnids. Neurohemal endocrine organs with structural and functional homology to the insect corpora cardiaca have been described for several arthropods (Scharrer and Scharrer, 1944; Gabe, 1952a, b, 1954a, b, c, 1955; Legendre, 1953, 1954). Among Ixodoidea, Gabe (1955) and Eichenberger (1970), working on Ornithodoros erraticus and 0. lahorensis, and 0. moubata, respectively, described paired “plaques paraganglionaires” as neurohemal organs in these ticks. During histological studies of the central nervous system of the adult Argas (Persicargas) arboreus Kaiser, Hoogstraal, and Kohls (Shoukrey and Roshdy, in preparation), we observed the neurohemal paraesophageal organ described here. MATERIALS AND METHODS Adult A. (P.) arboreus were taken from a NAMRU-3 Medical Zoology laboratory colony originating from rookeries of the heron Bubulcus i. ibis at the Nile Barrage near Cairo, and maintained according to the procedure of Kaiser (1966). Received for publication 27 October 1972. * From Research Project MF12.524.009-3010B, Bureau of Medicine and Surgery, Department of the Navy, Washington, D. C. The opinions and assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the Department of the Navy or of the naval service at large. This work was also supported in part by a special grant from the Office of Naval Research and by Agreement 03-005-01 between the NIAID (NIH) and NAMRU-3. t Department of Zoology, Faculty of Science, Ain Shams University, Cairo, and Medical Zoology Department, U. S. Naval Medical Research Unit No. 3 (NAMRU-3), c/o Spanish Embassy, Cairo, Arab Republic of Egypt. t Medical Zoology Department, NAMRU-3. ? Department of Entomology, North Carolina State University, Raleigh, North Carolina 27607. For histological studies, ticks were dissected in saline and the internal organs, including the central nervous mass, were removed directly into Bouin’s fixative. Tissues were dehydrated, cleared in xylene, and embedded in paraffin. Sections 5 to 6 u thick were stained with Mallory’s triple stain, azan, toluidine blue, chrome-hematoxylin-phloxine (CHP), and paraldehyde-fuchsin (PF); the latter stains are specific for neurosecretion (Gabe, 1955; Pearse, 1961). For electron microscopy, freshly dissected adult A. (P.) arboreus were fixed for 30 min in cold 2.5% glutaraldehyde buffered with 0.05 M sodium cacodylate containing 0.15 M sucrose. The central nervous mass and adjacent tissues were removed and placed in fresh fixative for 1 to 3 hr, washed for 12 hr in cacodylate buffer containing 0.3 M sucrose, postfixed in cold 1% osmium tetroxide in Millonig phosphate buffer (Millonig, 1961), and dehydrated in a graded series of cold ethanol. Material was then transferred through 3 changes of propylene oxide and embedded in Epon 812 (Luft, 1961). Thin sections, cut with a diamond knife on a Reichert Om U2 ultramicrotome, were double-stained with uranyl acetate and lead citrate (Venable and Coggeshall, 1965), and examined in a Siemiens Elmiskop 1A at 80 kv.