Ultrastructure of the Maxillary Organ of Scutigera coleoptrata (Chilopoda, Notostigmophora): Description of a Multifunctional Head Organ Gero Hilken 1 * and Jo ¨ rg Rosenberg 2 1 Central Animal Laboratory, University Duisburg-Essen Medical School, D-45122 Essen, Germany 2 Research Associate, Central Animal Laboratory, University Duisburg-Essen Medical School, D-45122 Essen, Germany ABSTRACT The maxillary organ of Scutigera co- leoptrata was investigated using light microscopy, elec- tron microscopy, and maceration techniques. Additionally, we compared the maxillary organ of S. coleoptrata with those of two other notostigmophoran centipedes, Parascu- tigera festiva and Allothereua maculata, using SEM. The maxillary organ is located inside the posterior coxal lobes of the first maxillae and extends posteriorly as sac-like pouches. The narrow epidermis of the maxillae is differ- entiated to form the epithelium of the maxillary organ. Two types of epithelia are distinguishable: a simple cuboi- dal epithelium of different height and differentiation (types I, II, IV) and a pseudostratified columnar epithe- lium (type III). These epithelia are covered by a highly specialized cuticle. The pseudostratified epithelium is the most prominent feature of the maxillary organ. It is cov- ered with hundreds of setae, protruding deep into the maxillary organ. Two different types of setae can be dis- tinguished, filiform and fusiform. The maxillary organ communicates with the oral cavity, the maxillary organ gland, the maxillary nephridium, and with a large number of epidermal glands that secrete into the maxillary organ. Epithelium III allows the extension of the maxillary organ when its pouches are filled with secretion. The maxillary organ is a complex multifunctional organ. The organ prob- ably stores excretion from the maxillary nephridia and secretory fluid from the maxillary organ gland and other epidermal glands. The fluid is primarily required as preening fluid. The ammonia of the excretory fluid is thought to evaporate via the setae and the wide opening of the maxillary organ. It is likely that parts of the fluid can be reabsorbed by the animal via the oral cavity. J. Mor- phol. 267:152–165, 2006. © 2005 Wiley-Liss, Inc. KEY WORDS: centipedes; maxillary organ; setae; maxil- lary nephridium, epidermal glands; maxillary organ gland; Parascutigera festiva; Allothereua maculata Inside the first maxillae of Scutigera coleoptrata is a large organ located in notostigmophoran chilo- pods. This organ was described as the “maxillary organ” by Haase (1884) due to its position. The or- gan is present in both sexes and is evident in the earliest anamorphic larval stages. It was first no- ticed by Latzel (1884), who described it as a struc- ture of unknown significance consisting of a large number of small hairs and microscopic spindle-like bodies. More detailed descriptions are given by Haase (1884) and Heathcote (1885), who both stated that this structure functions as an auditory organ. Initially, this view was shared by Verhoeff (1902– 25:39, 1904). Later, this hypothesis was rejected and it was suggested that the maxillary organ acts as a cleaning organ for preening antennae and legs (Ver- hoeff, 1902–1925:465; Manton, 1965; Desbalmes, 1987; Borucki, 1996). Using video recording, the function as a cleaning organ was recently rejected by Rosenberg et al. (2004). Borucki (1996) noted that the maxillary organ could be squeezed and retracted by different muscles. He compared the setae of the maxillary organ to tracheae and asked whether this organ could possibly have been developed from pairs of tracheal bundles. In addition, the organ may have other functions. As S. coleoptrata lives on the soil surface under relatively dry conditions, it is conceiv- able that these animals may have developed special adaptations to allow them to survive in dry condi- tions. Are these animals able to take up water from the surface using the setae of the maxillary organ? Unfortunately, there are contradictory observations whether or not the setae can be extended in vivo (Borucki, 1996; Rosenberg et al., 2004). Thus, the function of the maxillary organ and its components remains unclear. Until now, the maxillary organ has only been ex- amined by light microscopy. To date, there has been no detailed description of the maxillary organ and its relationship to other organs. The object of this study, therefore, was to conduct the first comprehen- sive investigation of the maxillary organ of Scuti- gera coleoptrata using electron microscopy (SEM, TEM) and maceration techniques in addition to light *Correspondence to: Priv.-Doz. Dr. Gero Hilken, Central Animal Lab- oratory, University Duisburg-Essen Medical School, Hufelandstrae 55, D-45122 Essen, Germany. E-mail: gero.hilken@uni-essen.de Published online 7 November 2005 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jmor.10392 JOURNAL OF MORPHOLOGY 267:152–165 (2006) © 2005 WILEY-LISS, INC.