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Abstract. The orchid Ophrys sphegodes Miller is pollinated by sexually excited males of the solitary bee Andrena nigroaenea, which are lured to the flowers by visual cues and volatile semiochemicals. In O. sphegodes, visits by pollinators are rare. Because of this low frequency of pollination, one would expect the evolution of strategies that increase the chance that males will visit more than one flower on the same plant; this would increase the number of pollination events on a plant and therefore the number of seeds produced. Using gas chromatography-mass spectrometry (GC-MS) analyses, we identified more than 100 compounds in the odor bouquets of labellum extracts from O. sphegodes; 24 compounds were found to be biologically active in male olfactory receptors based on gas chromatography with electroantennographic detection (GC-EAD). Gas chromatography (GC) analyses of odors from individual flowers showed less intraspecific variation in the odor bouquets of the biologically active compounds as compared to nonactive compounds. This can be explained by a higher selective pressure on the pollinator-attracting communication signal. Furthermore, we found a characteristic variation in the GC-EAD active esters and aldehydes among flowers of different stem positions within an inflorescence and in the n-alkanes and n-alkenes among plants from different populations. In our behavioral field tests, we showed that male bees learn the odor bouquets of individual flowers during mating attempts and recognize them in later encounters. Bees thereby avoid trying to mate with flowers they have visited previously, but do not avoid other flowers either of a different or the same plant. By varying the relative proportions of saturated esters and aldehydes between flowers of different stem positions, we demonstrated that a plant may take advantage of the learning abilities of the pollinators and influence flower visitation behavior. Sixty-seven percent of the males that visited one flower in an inflorescence returned to visit a second flower of the same inflorescence. However, geitonogamy is prevented and the likelihood of cross-fertilization is enhanced by the time required for the pollinium deposited on the pollinator to complete its bending movement, which is necessary for pollination to occur. Cross-fertilization is furthermore enhanced by the high degree of odor variation between plants. This variation minimizes learned avoidance of the flowers and increases the likelihood that a given pollinator would visit several to many different plants within a population.

Ophrys flowers mimic virgin females of their pollinators, and thereby attract males for pollination. Stimulated by scent, the males attempt to copulate with flower labella and thereby ensure pollination. Here, we show for the first time, to our knowledge, that pollinator attraction in sexually deceptive orchids may be based on a few specific chemical compounds. Ophrys speculum flowers produce many volatiles, including trace amounts of (omega-1)-hydroxy and (omega-1)-oxo acids, especially 9-hydroxydecanoic acid. These compounds, which are novel in plants, prove to be the major components of the female sex pheromone in the scoliid wasp Campsoscolia ciliata, and stimulate male copulatory behaviour in this pollinator species. The specificity of the signal depends primarily on the structure and enantiomeric composition of the oxygenated acids, which is the same in wasps and in the orchids. The overall composition of the blend differs significantly between the orchid and its pollinator and is of secondary importance. 9-Hydroxydecanoic acid is a rarely occurring compound that until now has been identified only in honeybees. Contrary to the standard hypothesis that Ophrys flowers produce only 'second-class attractivity compounds' and are neglected once the pollinator females are present, we show that flowers are more attractive to the males than are their own females.

According to molecular sequence data Crustacea and not Myriapoda seem to be the sister‐group to Insecta. This makes it necessary to reconsider how the morphology of their eyes fit with these new cladograms. Homology of facetted eye structures in Insecta (Hexapoda in the sense of Ento‐ and Ectognatha) and Crustacea is clearly supported by identical numbers of cells in an ommatidium (two corneageneous or primary pigment cells, four Semper cells which build the crystalline cone and primarily eight retinula cells). These cell numbers are retained even when great functional modification occurs, especially in the region of the dioptric apparatus. There are two different possibilities to explain differences in eye structure in Myriapoda depending on their phylogenetic position in the cladogram of Mandibulata. In the traditional Tracheata cladogram, eyes of Myriapoda must be secondarily modified. This modification can be explained using the different evolutionary pathways of insect facetted eyes to insect larval eyes (stemmata) as an analogous model system. Comparative morphology of larval insect eyes from all holometabolan orders shows that there are several evolutionary pathways which have led to different types of stemmata and that the process always involved the breaking up the compound eye into individual larval ommatidia. Further evolution led on many occasions to so‐called fusion‐stemmata that occur convergently in each holometabolic order and reveals, in part, great structural similarities to the lateral ocelli of myriapods. As myriapodan eyes cannot be regarded as typical mandibulate ommatidia, their structure can be explained as a modified complex eye evolved in a comparable way to the development to the fusion‐stemmata of insect larvae. The facetted eyes of Scutigera (Myriapoda, Chilopoda) must be considered as secondarily reorganized lateral myriapodan stemmata, the so‐called ‘pseudo‐compound eyes’. New is a crystalline cone‐like vitreous body within the dioptric apparatus. In the new cladogram with Crustacea and Insecta as sister‐groups however, the facetted eyes of Scutigera can be interpreted as an old precursor of the Crustacea – Insecta facetted eye with modified ommatidia having a four‐part crystalline cone, etc. as a synapomorphy. Lateral ocelli of all the other Myriapoda are then modified like insect stemmata. The precursor is then the Scutigera‐Ommatidium. In addition further interpretations of evolutionary pathways of myriapodan morphological characters are discussed.

Zusamrnenfassung Im letzten Jahrzehnt sind eine Reihe von Klassifikationen der Chelicerata veröffentlicht worden, die nicht auf Synapomorphien gründen. Das Ziel der vorliegenden Untersuchung ist ein cladistisches System und eine plausible Vorstellung von der Entfaltung der Chelicerata. Zum Grundbauplan der Chelicerata gehört ein ungeteiltes Prosoma mit sechs extremitätentragenden Segmenten sowie ein Opisthosoma aus 12 Segmenten und dem Tergaldorn eines reduzierten 13. Segmentes. Es gibt keinen Hinweis darauf, daß die Scorpiones ein Tergit reduziert haben; ihre 12 Tergite entsprechen den ursprünglichen 12 Opisthosomasegmenten. Jedoch werden die ventralen Teile der Anlage des zweiten Opisthosomasegmentes sekundär unterteilt. Diese Unterteilung und die daraus entstehenden Kämme mit ihren Ganglien und Blutgefäßen stellen eine Synapomorphie der Scorpiones dar. Ein Schlüsselereignis in der Evolution der Chelicerata ist die Entwicklung der räuberischen Lebensweise. Sie hat zur Verkürzung der ursprünglichen ventralen Nahrungsrinne geführt. Die Extremitäten des ersten Opisthosomasegmentes (Chilaria, Metastoma) übernehmen zunächst die hintere Begrenzung der Nahrungsrinne bzw. des daraus entstehenden Mundvorraumes. Zahlreiche mohologische, ultrastrukturelle, entwicklungsgeschichtliche und ethologische Merkmale werden darauxin untersucht, ob sie Synapomorphien zur Begründung eines cladistischen Systems liefem. Neben den klassischen morphologischen Merkmalen ergaben besonders die Feinstruktur der Spermatozoen und der Lichtsinnesorgane überzeugende Synapomorphien. Das Ergebnis dieser Unter‐suchungen ist das Cladogramm (I) (S. 179/180) und die ihm zugrunde liegenden Synapomorphien (Tab., S. 178/179). Die wichtigsten Folgerungen sind: 1. Die Chelicerata sind ein monophyletisches Taxon; ihre Schwestergruppe sind die Olenellida. 2. Die Aglaspida sind die plesiomorphe Schwestergruppe aller übrigen Chelicerata (Euchelicerata). 3. Innerhalb dieser sind die Xiphosurida die plesiomorphe Schwestergruppe aller übrigen Chelicerata (Metastomata). 4. Diese spalten sich früh in die Eurypterida und Arachnida. Die Arachnida sind also eine mono‐phyletische Gruppe, und wahrscheinlich ist schon ihre Stammform zum Landleben übergegangen. 5. Innerhalb der Arachnida sind die Ctenophora oder Pectinifera (einzige Ordnung: Scorpiones) die Schwestergruppe aller übrigen (epectinaten) Arachniden (Lipoctena). 6. Innerhalb der Lipoctena sind die Uropygi, Amblypygi, Araneae (Megoperculata) die Schwestergruppe der übrigen Ordnungen, die als Apulrnonata zusammengefaßt werden. 7. Die Pantopoda werden als Chelicerata aufgefaßt, doch 1äßt sich zur Zeit nicht entscheiden, ob sie als die Schwestergruppe aller anderen Chelicerata angesehen werden müssen oder als die Schwestergruppe der Euchelicerata. Summary Studies on the morphology, taxonomy and phylogeny of the Chelicerata. Part I and II The aim of the present investigation is to present a cladistic classification of the Chelicerata based on synapomorphies and to develop plausible ideas on the evolution of the Ch...