| One might ask what one could possibly gain from exploring the function of tiny larval eyes? And one might answer that an exploration of the structure of such eyes and of the mechanical properties that evolved under their taxing size constraints has already served to inspire engineers in devising novel methods of navigation and visual task performance in robots. Moreover, an exploration of their specializations has also served to facilitate the study of very particular aspects of vision that can be found across many other species, including vertebrate animals and humans.;Thus far, attention has been largely focused on adult compound eyes, but invertebrates also have chambered eyes, which should probably merit no less attention. Contrary to what is generally thought about these eyes, some of these visual systems are highly developed and complex. They too may result in the discovery of novel visual mechanisms, which may also serve to inspire engineers or to provide us with a more complete understanding of vision as well as of the evolution and development of eyes in general.;Among the most interesting of these eyes are the principal eyes, E1 and E2, of Thermonectus marmoratus (Coleoptera:Dytiscidae) larvae. In previous studies of the behavior of these larvae, the anatomy of their eyes, the spectral sensitivity of their retinas and the ultrastructure of the retina of their principal eyes, their visual system have been shown to be unlike any other known eyes. They are unique in that they are tubular in shape and have a very complex layered retina in which the photoreceptor cells of the proximal retina (PR) are sensitive to UV light while those of the distal retina (DR) are sensitive to green light. The DR consists of many layers of photoreceptor cells whose rhabdomeric portions are oriented perpendicular to the light path. Additionally, the retina is linear with a visual field that is a horizontal stripe. Due to the highly unusual construction of these eyes, some of the results were hard to interpret and raised additional questions as to how these eyes actually functioned in the context of both the behavior of the larvae and the visual challenges with which they were faced.;For the purposes of this dissertation, a series of experiments was carried out to address the questions raised by the aforesaid past results and to elaborate a first conceptual model of how these eyes might function (Chapter 5). To that end, the optical properties of the lenses of these eyes were measured in order to ascertain where images are focused within these eyes, based on object distance and the spectral sensitivity of the retina (Chapter 2 and 4). The polarization sensitivity of the proximal retina was also measured (Chapter 3) for confirmation of its polarization sensitivity as suggested by the ultrastructure of its cells. |
