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Though pain scientists now understand pain to be a complex experience typically composed of sensation, emotion, cognition, and motivational responses, many philosophers maintain that pain is adequately characterized by one privileged aspect of this complexity. Philosophically dominant unitary accounts of pain as a sensation or perception are here evaluated by their ability to explain actual cases—and found wanting. Further, it is argued that no forthcoming unitary characterization of pain is likely to succeed. Instead, I contend that both the motivating intuitions behind unitary accounts and the wide range of pain phenomena are best accommodated by a componential view of pain that does not privilege any single component as necessary or sufficient.

Many species of copepods form dense aggregations, known as swarms. In the laboratory, we experimentally induced 5 different species of copepod to swarm in response to a point source of light. To map out the (x, y z, t) positions of swarm members, 2 right-angle views of the 3-dimensional swarm were videotaped. Since images of individual copepods appear indistinguishable on the paired 2-dimensional projections, an algorithm was developed which matched the temporal changes of the vertical (z) positions of all images from the 2-dimensional projections of the 3-dimensional copepod movement to produce (x, y, z, f) positions of each individual. With the temporal/spatial positional data of swarm members, we tested the hypothesis that the fluid disturbance surrounding individual moving copepods, rather than the exoskeleton, maintains minimum separation distance. As the density of the swarm increased, the average nearest-neighbor distance NND decreased, as did the mean minimum NND (MNND). For 3 of the 5 species, the MNND was significantly greater than that predicted from a random distribution, and was greater than twice the antennule or prosome length. While occasional physical contact may occur, resulting in escapes or attempted mating, it appears that most swarm members remain outside the field of self-generated fluid motion in the boundary layers surrounding their neighbors.

The behavior of sighted and of blind male and female Rabidosa rabida paired in various combinations was videotaped and analyzed. When walking, neither sighted nor blind spiders could detect motionless conspecifics prior to contact. When motionless, blind males detected moving females at greater distances than they detected moving males. However, neither sighted nor blind motionless males detected very slowly moving females at any distance. These data suggested for R. rabida: (1) the effectiveness of visually and vibrationally cryptic locomotion, (2) a lack of form vision, and (3) absence of a close-range, air-borne pheromone. In both sexes, visual detection of moving conspecifics by motionless spiders provided for accurate orientation responses at greater distances than did mechanoreception. Nonetheless, blind females could orient accurately toward courting males at close range based on vibrations. Blind males showed courtship display when briefly contacted by another male, suggesting an inadequate chemically based sex-recognition mechanism. Sighted males showed courtship display after visually detecting a walking male, but did not do so in response to a courting male, i.e., mutual courtship did not occur. Blind males sometimes did perform mutual courtship, suggesting an inadequate vibratory recognition mechanism. Unlike salticids, these lycosids did not require vision to initiate either agonistic display or ritualized fighting.

Diaptomus minutus Lilljeborg, 1889, and Cyclops scutifer Sars, 1863, detected the hydromechanical signals created by small moving spheres of sizes comparable to those of most crustacean zooplankters (∼ 1 mm). The number of escapes and escape distance were affected by the size, location, and direction of movement of the spheres. Ability to detected and flee from the moving spheres was not significantly affected by ambient turbulence. The herbivorous D. minutus escaped from all hydromechanical signals. The predaceous Cyclops scutifer showed higher escape probability from large signals and occasionally recognized small signals as prey. /// Diaptomus minutus Lilljeborg, 1889 et Cyclops scutifer Sars, 1863 ont détecté les signaux hydromécaniques créés par des petites sphères mobiles de tailes comparables à celles de la plupart des crustacés zooplanctoniques (∼ 1 mm). Le nombre d'échappées et la distance d'échappée étaient affectés par la taille, la localisation et la direction de mouvement des sphères. La capacité de détecter et de fuir les sphères mouvantes n'était pas affectée de façon sigificative par la turbulence ambiante. L'herbivore Diaptomus minutus fuyait tous les signaux hydromécaniques. Le prédateur Cyclops scutifer manifestait la plus haute probabilité d'échappée aux grands signaux et, occasionnellement, reconnaissait les petits signaux comme des proies.

The ability of an erpobdellid leech, Erpobdella montezuma, to discriminate between two congeneric amphipod prey (Hyalella montezuma and Hyalella azteca) through mechanoreception was examined. Both E. montezuma and H. montezuma, a pelagic filter feeder, are endemic to the near thermally constant environment of Montezuma Well, Arizona, and form a highly specialized predator-prey relationship. In contrast, H. azteca, a benthic detritivore, is widely distributed throughout North America. Erpobdella montezuma was highly responsive to the prey signals of the endemic H. montezuma and showed only a limited response to H. azteca. An inverse relationship occurred between the frequency of attack and size of the leech. The abilities of Erpobdella punctata and Nephelopsis obscura, neither found in Montezuma Well, to detect the signals of both amphipod prey were also examined. These species with non-specialized diets showed a low response to the signals of both prey species. This study demonstrates that very close predator-prey relationships can develop over evolutionary time in isolated aquatic systems through the use of mechanoreception.

Mechanoreception can be considered as a fundamental sensory modality developed in all animal phyla. In tetrapods it comprises the auditory system (Hetherington, chapter 12 in this volume; Nummela, chapter 13 in this volume), the lateral line system of amphibians (not covered in this section, but see Bleckmann, 1994; Coombs et al., 1989), and somatosensory systems. Generally, the somatosensory system of secondarily aquatic tetrapods can be divided into the spinal system innervating the body surface, deep tissues, and extremities, and the trigeminal system innervating facial areas such as the muzzle of mammals or the beak of birds. In the next chapter,

La cuticule des Crustacés porte des extrusions qui sont parfois impliquées dans des méchanismes adhésifs. C'est le cas des \"cincinnuli\", minuscules phanères constituées d'une tige courbe terminée par une tête élargie. Dans ce travail, des cincinnuli sont examinés chez les crevettes Palaemonetes varians (Leach, 1814) et Palaemon serratus (Pennant, 1777) à l'extrémité de l'appendix interna, une formation des endopodites de paires II à V de pléopodes. Ils forment un groupe d'environ 40, chacun avec un axe crochu d'environ 15 μm et portant une tête en quart de sphère. Lorsque les extrémités des deux appendices internae de la même paire entrent en contact, elles adhèrent grâce à l'entremêlage des cincinnuli, mais elles peuvent se séparer par un mouvement latéral. Chez le mâle de la crevette Penaeus japonicus Bate, 1888, les endopodites de la première paire de pléopodes sont fermement réunis par plusieurs milliers de cincinnuli anchoriformes. Des structures en brosse réalisent un autre type d'accrochage, observé ici entre les deux maxillipèdes d'Isopodes terrestres et, chez les mâles, sur les endopodites de la première paire de pléopodes. L'entremêlage des structures en brosse aboutit à une liaison lâche. Au contraire, des liaisons très solides sont réalisées, également chez les mâles d'Isopodes terrestres, par des coaptations entre l'apophyse génitale et les endopodites de la première paire de pléopodes. Ces coaptations ne sont pas liées à la présence de phanères spécialisées mais à la forme et aux replis de la cuticule. Ces diverses structures adhésives, dont la signification adaptative est discutée, rappellent des systèmes utilisés dans l'industrie et peuvent servir de modèles pour de nouvelles réalisations.

Sensilla of the predaceous fresh-water leech Erpobdella montezuma were examined by scanning and transmission electron microscopy. Densities of sensilla and cilia within each sensillum were highest in the anterior-most annulus and were less in more posterior annuli. The most dramatic decrease was between annulus 1 and 3; there was little difference in densities of each from midbody to the posterior region. The highest densities of sensilla were found on the posterior sucker ($\\bar x = 48.0 \\times 10^{3}/cm^2$) and annullus 1 ($\\bar x = 36.1 \\times 10^{3}/cm^2$). In our preparations, cilia near the mouth and on the sucker were flush with the epidermal surface, but those in other regions protruded. Arrangement of G (grouped) and S (single) cilia along the longitudinal axis of the leech are described; the G cilia typically comprise 70-90% of the total, except on the dorsal posterior end where G cilia are ca. 46% of the total. The ultrastructure of G and S cilia was examined. Feeding experiments comparing response to prey species that swim in the water column with response to a more benthic congeneric prey species suggests that movement by prey is important in their detection by this leech. We postulate that the sensilla are important in detecting these movements.