January 12 COVER Scanning electron micrograph of Trichomonas vaginalis parasites (gray-green) adhering to vaginal epithelial cells (pink). Attached parasites are flattened and amoeba-like; parasites that do not adhere are pear-shaped. See page 207. Image: Antonio Pereira-Neves and Marlene Benchimol, Santa Ursula University, Rio de Janeiro

January 26 COVER Mouse zygotes that are developing parthenogenetically (without fertilization) with a single polar body and two pronuclei. These zygotes develop into blastocysts, from which embryonic stem cells can be harvested. Such cell lines can provide a source of immunologically compatible tissues for transplantation. Zygote outer diameter, 70 to 80 micrometers. See page 482. Image: K. Kim, K. Ng, A. Yabuuchi, and G. Q. Daley

February 23 COVER Projectile points of the prehistoric Clovis complex of North America are characterized by their lanceolate shape, concave base, distinctive basal flute, and basal edge grinding. The large point in the middle shows the distinctive outrepassé flaking pattern (broad flakes that extend across the width of the point) often found on Clovis points and other bifaces. See page 1122. Photo of casts: Charlotte D. Pevny

March 2 COVER In adult humans, newly born brain cells travel in the rostral migratory streams (orange bands) from the fluid-filled lateral ventricles (pink structures at top) to the olfactory bulbs, along hollow tubelike extensions of the ventricles. See page 1243. Image: Jonathan Westin

March 9 COVER A scanning tunneling microscopy image of a high-temperature superconductor (bottom) shows the regular atomic periodicity of the crystal. Simultaneously measured ratios of electron injection to extraction (top, yellow) reveal strong variations in electronic structure. See page 1380. Image: Yuhki Kohsaka

March 23 COVER Part of the cylindrical Compact Muon Solenoid particle detector descends to a hall 100 meters underground at the European particle physics laboratory CERN. The detector will capture the hail of particles produced when CERN’s Large Hadron Collider smashes protons at unprecedented energies. A special News report beginning on page 1652 profiles the new collider. Photo: Maximilien Brice, CERN

March 30 COVER A bloom of Rafflesia tuan-mudae from western Borneo. Rafflesiaceae species produce the world’s largest flowers, with blooms up to 1 meter in diameter. Molecular evidence described on page 1812 shows that these enigmatic parasites are members of the spurge family, Euphorbiaceae, hence the enormous flowers of Rafflesiaceae most likely arose from tiny-flowered ancestors. Photo: © Ch’ien Lee

April 6 COVER A Chihuahua walking with a Great Dane more than 50 times its mass. The extreme diversity in body size among purebred dogs is greater than that of any other mammalian species. Researchers have identified a gene that helps explain this size diversity. See page 112. Photo: Deanne Fitzmaurice

April 20 COVER Male germline stem cells (red and green) from mice produce spermatozoa after transplantation to the seminiferous tubules of recipient mice. See the special section on germ cells beginning on page 387. Photo illustration: J. Hayden, RBP, H. Kubota, and R. L. Brinster

April 27 COVER Microscopic marine plants (Chaetoceros, a chain-forming diatom) are consumed by zooplankton animals (Neogloboquadrina, a foraminifera, lower inset; tail of Neocalanus copepod, upper inset). Marine plankton food webs can affect climate by regulating the removal of carbon dioxide in surface waters and transporting this carbon to the deep sea via sinking particles. See page 567. Photos: Mary Silver

May 4 COVER Artist’s conception of Mercury, with a cutaway showing the molten core revealed by high-precision radar data. This finding will help to understand the internal structure, thermal evolution, and magnetic field generation of terrestrial planets. Mercury’s surface is from Mariner 10 images. See page 710. Image: Christopher Bickel/Science

May 11 COVER A bat, Glossophaga soricina, in flight within a wind tunnel. The air velocity field induced by the wingbeat is shown by superimposed arrows and to scale. The reconstructions of the wake produced by bat flight, reported on page 894 have features that are not observed in the wakes of similarly sized birds. Image: L. C. Johansson, M. Wolf, and A. Hedenström

May 25 COVER Artist’s rendition of a model protein, trypsin, experiencing a force. Experimental and computational techniques that apply force to single biological macromolecules provide insight into molecular properties and suggest how mechanical forces may transduce signals in cells. See the special section on single molecules beginning on page 1143. Image: Christopher Bickel/Science

June 22 COVER A female Aedes aegypti mosquito attempts to take flight after a blood meal. The complete sequencing of this disease vector is reported on page 1718, with an accompanying Perspective on page 1703. Photo: James Gathany/CDC

August 3 COVER A showcase of cellular weapons deployed by the immune system ranges from antibody-making B cells to macrophages. A special section beginning on page 611 outlines the outstanding challenges in immunology for understanding how immune cells protect and sometimes injure us. Illustration: Christopher Bickel

August 10 COVER An array of multilayer mirrors compresses ultrabroadband laser pulses (orange beam) to 1.5 wave cycles. The attosecond x-ray pulses produced with them allow the control and real-time observation of atomic-scale electron motion. See the special section on attosecond spectroscopy beginning on page 765. Photo: Thorsten Naeser for Max Planck Institute for Quantum Optics/Laboratory for Attosecond and High-Field Physics

September 14 COVER Supercomputer simulation of the filamentary environment in which the very first stars formed, 100 million years after the Big Bang. The filaments, about 9000 light-years in length, are characteristic of a model universe in which the dark matter consists of fast-moving elementary particles. See page 1527. Image: Liang Gao and Tom Theuns, Institute for Computational Cosmology, Durham University

September 28 COVER The red alga Chondrus crispus (Irish moss). This image, taken with a digital point-and-shoot camera, tied for first place in the photography category of the National Science Foundation/Science 2007 Visualization Challenge. All the winning entries are displayed in a special feature beginning on page 1857 and online at www.sciencemag.org/sciext/vis2007. Image: Andrea Ottesen

October 5 COVER Artist’s representation of the molecular signaling initiated by cell surface receptors. Four Perspectives in this issue and their associated Connections Maps in Science‘s STKE highlight pathways that regulate diverse functions–from cell motility and survival to development in mammals, plants, and insects. See the special section beginning on page 61. Illustration: Chris Bickel/Science

October 19 COVER Structure of a gold nanoparticle in which the central atoms are packed in a decahedron, surrounded by additional layers of gold atoms in unanticipated geometries. Gold atoms, gold; sulfur atoms, blue; carbon atoms, white; oxygen atoms, red; the superimposed red mesh depicts the electron-density distribution determined by x-ray crystallography. See page 430. Image: Pablo D. Jadzinsky and Guillermo Calero

November 9 COVER All-sky projection of highest-energy cosmic rays detected by the Pierre Auger Observatory (open circles) that are correlated with the positions of nearby quasars (crosses), a measure of the local galaxy distribution. The supergalactic and Milky Way planes are marked. The background shows a composite image of a nearby galaxy (M82) observed by NASA’s Spitzer, Hubble, and Chandra space observatories. See page 938. Composite image: Kelly Krause/Science (figure: Auger Collaboration; photo: NASA/JPL-Caltech/STScI/Chandra X-ray Center/Univ. of Arizona/ESA/AURA/Johns Hopkins Univ.)

November 23 COVER Structure of the human β2-adrenergic receptor (red) embedded in a lipid membrane and bound to a diffusible ligand (green), with cholesterol (yellow) between the two receptor molecules. A cartoon of the lipidic cubic phase used for crystallization of the receptor is shown in the background. See pages 1258 and 1266. Image: Yekaterina Kadyshevskaya and the Stevens Laboratory, Scripps Research Institute

November 30 COVER The cell nucleus houses the genetic blueprint, but it is also a dynamic organelle that interacts with the rest of the cell on many levels. A special section beginning on page 1399 focuses on the cell biology of the nucleus. Image: Chris Bickel/Science

December 14 COVER Coral polyps with exquisite coral pigments (pocilloporin) remain after bleaching of the southern Great Barrier Reef around Great Keppel Island (Wappaburra), a result of elevated sea temperatures in January 2006. During heat stress, the symbiosis between corals and dinoflagellates fails, leading to mass exodus of the brown plant-like symbionts from the tissues of the coral host. See the Editorial on page 1695, the News Focus on page 1712, and the Review on page 1737. Image: Ove Hoegh-Guldberg, University of Queensland