Excerpt: Regrettably, phenomenologists who concentrate narrowly on the early Husserl of the Logical Investigations (1900–1901; Husserl 2001a) and Ideas I (Husserl 1977a) often overemphasize his focus on the individual life of intentional consciousness as reconstructed from within (and even on the structure of individual, atomistic lived experiences [Erlebnisse]) and tend to overlook Husserl’s original, radical, and fundamentally groundbreaking explorations of intersubjectivity, sociality, and the constitution of historical cultural life (which would later influence Heidegger and Schütz, among others). In respect of this individualist misinterpretation, Husserl is often his own worst enemy, since he repeatedly and very publicly, for example, in his Cartesian Meditations (Husserl 1950, 1967; hereafter CM), compared his phenomenological breakthrough to subjectivity with Descartes’s discovery of the ego cogito and modeled his phenomenological epoché, albeit with important changes of emphasis, on Descartes’s radical doubt. As a result, Husserl’s phenomenology has too often been designated a methodological solipsism that proceeds through individualistic introspection of conscious experiences, and Husserl’s wider explorations of social and cultural life have been passed over (and many of his original discoveries have been attributed to others, e.g., Heidegger and Gadamer). It is worth reminding ourselves, therefore, of the originality of Husserl’s meditations on the nature of the self, its embodiment, and its intercorporeal, intersubjective communal relations with others. In this chapter, then, I want to focus on Husserl’s mature reflections (i.e., as specifically found in his writings of the 1920s and 1930s) on the intentional constitution of culture, particularly as he understood it to relate to lived embodiment and, especially, the specific relations that hold between lived bodies, their Ineinandersein, Füreinandersein, or what Husserl calls in Cartesian Meditations “a mutual being-for-one-another” (ein Wechselseitig-füreinander-sein; CM, 129; Hua I, 157). As he puts it elsewhere, in the Crisis of European Sciences (Husserl 1970, 1962), Husserl approaches human subjects not only as having “subject being for the world” (Subjektsein für die Welt) but also as possessing “object being in the world” (Objektsein in der Welt; Crisis, 178; Hua VI, 182). How humans can be both in the world and for the world is, for him, the riddle of transcendental subjectivity.

Cockroach legs bear tactile spines equipped with campaniform sensilla – mechanoreceptors associated with the cuticle – which function by a single bipolar neuron from whose dendrite tip extends a modified cilium packed with 350–1000 parallel cytoplasmic microtubules. These microtubules, which can be chemically disassembled with colchicine and vinblastine, are intimately associated with the site of mechanical stimulation. Treatment of living sensilla with colchicine and vinblastine abolishes their ability to respond to mechanical stimulation 1–2 hr after drug application. Loss of function is accompanied by large-scale disassembly of microtubules in the modified cilium. The experimental evidence strongly suggests that microtubules play an important role in the process of sensory transduction in campaniform sensilla.

This paper, the first in a series concerning the neurobiology of sensory cilia, describes the ultrastructure of our chosen model system – the proximal femoral chordotonal organ (FCO) in pro-and mesothoracic grasshopper legs. The FCO is a bundle of 150–200 longitudinally oriented chordotonal sensilla. Each chordotonal sensillum is a mechano-receptive unit that contains two bipolar neurons whose dendrites bear sensory cilia. The structure of the sensory cilia leads us to suggest that they are motile cilia that respond to the mechanical stimulus with an “active stroke” which excites a transducer membrane at the dendrite tip.

This paper describes the ultrastructural modifications that cockroach campaniform sensilla undergo at three major stages in the molting cycle and finds that the sensilla are physiological functional at all developmental stages leading to ecdysis. Late stage animals on the verge of ecdysis have two completely separate cuticles. The campaniform sensillum sends a 220-mum extension of the sensory process through a hole in its cap in the new (inner) cuticle across a fluid-filled molting space to its functional insertion in the cap in the old (outer) cuticle. Mechanical stimulation of the old cap excites the sensillum. The ultrastructural geometry of late stage sensilla, coupled with the observation they are physiolgically functional, supports the hypotheses (a) that sensory transduction occurs at the tip of the sensory process, and (b) that cap identation causes the cap cuticle to pinch the tip of the sensory process, thereby stimulating the sensillum.

Combined high-voltage electron-microscopic and electrophysiological studies strongly suggest that cilia play an active role in sensory transduction in the grasshopper proximal femoral chordotonal organ (FCO) a ciliated mechanoreceptor. The FCO of proand mesothoracic legs of Melanoplus bivittatus contains a group of several hundred chorodontal sensilla arranged in a near-parallel bundle and slung between the proximal femur and the knee joint. Both flexion and extension of the tibia stimulate the FCO, which appears to measure the femoro-tibial angle. The FCO’s U-shaped response curve indicates that progressive flexion or extension from the resting joint angle of 90 degrees increases the response frequency of individual receptors and recruits additional units as well. Since the FCO is a purely tonic mechanoreceptor, it is possible to fix FCOs during maximum and minimum states of stimulation and electron-microscopically observed changes in the receptor’s fine structure. The most conspicuous change is the production of a pronounced bend at the base of the sensory cilia in chordotonal sensilla of maximally stimulated femoral chordotonal organs.

The main purpose of this paper is to describe the mutual control relations between ciliary movements and molecular events in the axoneme. These control relations are expressed mathematically through a cusp-catastrophe description between angular movements and active sliding. The parameters are defined so that they are widely applicable and accessible to experimentation. A choice of parameters is tested on the basis of Satir’s studies on active sliding, the energetics of ciliary beating, and the dependency on ATP for beat amplitude. For all these cases a good predictive fit is found. Further application and connections of the proposed control model are discussed.

1. Mechanical stimulation of individual tibial campaniform sensilla produces specific reflex effects upon motoneurones to leg muscles. 2. The reflex effects of a campaniform sensillum depend upon the orientation of its cuticular cap. The proximal sensilla, oriented perpendicular to the long axis of the tibia, excite slow motoneurones to the extensor tibiae and extensor trochanteris muscles and inhibit slow motoneurones to the flexor tibiae and flexor trochanteris muscles. The distal sensilla, oriented parallel to the tibia, exhibit reflexes of opposite sign, inhibiting the extensors and exciting the flexors. 3. These reflexes constitute a negative feedback system. Individual sensilla specifically excite motoneurones which innervate muscles whose resultant tensions decrease the firing of those sensilla. 4. It is postulated that individual campaniform sensilla can detect loading of the leg in various postures and can excite appropriate motoneurones in compensation. These receptors can also detect strains caused by large, resisted contractions of the antagonist muscles and inhibit the corresponding motoneurones.