Masutaro Kuwabara

The fine structure of the compound eye of a damsel-fly

SummaryThe compound eyes of two species of damsel-flies, Ishunura senegalensis and Cersion calamorum, were examined by electron microscopy. Each ommatidium is composed of eight retinula cells which are semistratified in the receptor layer. The retinula cells are divided into four types from the difference of levels in the rhabdom formation; one distal large cell having the rhabdomere only in the distal layer, four middle cells forming the rhabdom in the middle layer, two proximal cells making up the rhabdom in the proximal layer and one distal small cell having no rhabdomere in any layers. In addition, the lamina ganglionaris was partly observed. Some retinula axons terminate at an different level from the other axons. The functional differentiation among these different types of cells is discussed with relation to the analysis of the polarized light and the discrimination of the diffraction images.

Synaptic organization of the fleshfly ocellus

SummaryThe synaptic organization of the fleshfly (Boettcherisca peregrina) ocellus has been studied by transmission electron microscopy. Three types of neuronal element are recognized in the ocellus: (1) 70–100 retinula axons (2) four thick ocellar nerve fibres and (3) several thin ocellar nerve fibres. Synaptic connections accompanied by characteristic presynaptic ribbons have been found between these three elements in five combinations. Four of these are numerous (retinula axons synapsing onto thick ocellar nerve fibres or onto thin ocellar fibres; thin ocellar nerve fibres synapsing onto thick ocellar nerve fibres or onto other thin ocellar fibres). One or two of the thin ocellar nerve fibres are mainly presynaptic elements. The remaining thin fibres are both pre- and postsynaptic. These observations suggest that the thick ocellar nerve fibres are afferent and at least one or two of the thin ocellar nerve fibres are efferent. The function of the remaining thin fibres is not known. The fifth combination is a feedback synapse from thin ocellar nerve fibres onto retinula axons. In addition, neuro-glial synapses have been found between thin ocellar nerve fibres and glial cells. The latter two combinations are less common and may provide alternative neuronal pathways for processing ocellar input.

The rhabdomeric microvilli of several arthropod compound eyes kept in darkness

SummaryElectron microscopical studies were made on the fine structure of the rhabdomeric microvilli of the compound eyes of seven species of arthropods (Procambarus, Neocaridina, Caridina, Potamon, Artemia, Diestrammena, Drosophila) raised in complete darkness for 1–8 months or for successive generations, using various fixation techniques.The rhabdomeric microvilli of the individuals kept in darkness for a long period were regularly arranged as in normal eyes in the material prepared by double fixation with glutaraldehyde and OsO4, whereas in those fixed solely by OsO4 various forms of vesiculations were seen. The structural changes of the rhabdomere in darkness, which have been reported by several workers, were conceived to be an artefact caused by OsO4 fixation.

Regulation of insect brain excitability by ocellus

SummaryUnitary discharges were recorded from various areas of the brain in the fleshfly (Boettcherisca peregrina), whose compound eyes were occluded to light but the ocelli were exposed to it.1.Giving olfactory and mechanical stimulation to the antenna, the excitatory and the inhibitory neurones were found. In the excitatory neurones the unitary discharges appeared during the stimulation or the spontaneous discharges were increased by it. Phasic responses were found mostly in the protocerebrum, and tonic ones were in the deutocerebra, tritocerebra and the suboesophageal ganglion. In the inhibitory neurones the spontaneous discharges disappeared during the stimulation. The inhibition of the discharge was tonic in the deuto- and tritocerebra.2.When the ocelli were illuminated, the frequency of the spontaneous discharges was increased in many units and was decreased in some units.3.By turning off the illumination to the ocelli, the unitary response to the antennal stimulation was decreased (light facilitatory unit) in most units of the protocerebrum, while it was increased (light occlusive unit) in most units of the deutocerebra, tritocerebra and the suboesophageal ganglion.4.By darkening the ocelli, the latency of the unitary response was prolonged in most of the light facilitatory units, while it was shortened in the light occlusive units.5.The light facilitatory units were mainly found in the medial region of the brain, and the light occlusive units were in the dorsal region of the protocerebrum and in the ventral region of the deutocerebra, tritocerebra and the suboesophageal ganglion. The results suggest that the ocelli regulate the brain activity.

Convergence of antennal and ocellar inputs in the insect brain

SummaryUnitary responses were recorded from the brain of the fleshfly, Boettcherisca peregrina, during olfactory or mechanical stimulation of the antenna, and simultaneous photic stimulation of the ocelli. Convergence from the two inputs, the antenna and the ocelli, was observed. The response to antennal stimulation was facilitated by photic stimulation in most units. The responses to the antennal stimuli were facilitated greatly at the peak of the photic response. Some units responded both to ocellar illumination and antennal stimulation. Their response to antennal stimulation seemed independent of the light-condition during the light-adapted state, but was facilitated at the onset of the ocellar illumination, and occluded just after its cessation. In addition, there were some units which responded to antennal stimulation but not to the ocellar illumination; some of them also showed facilitation of the response to antennal stimulation during ocellar illumination.

The function of photoexcitive neurones in the central ganglia for behavioral activity of the marine mollusc,Onchidium verruculatum

Summary1.The function of the photoexcitive neurones located within the CNS in the marine pulmonate mollusc,Onchidium verruculatum was investigated.2.A light-evoked discharge was recorded from the photoexcitive neurones in the whole animal preparation (Fig. 3).3.Tactile stimuli from the mantle were mediated synaptically to the photoexcitive neurones through the pleuro-parietal nerves of both sides (Fig. 4).4.An attempt was made to confirm the tactile receptive field of the photoexcitive neurones, Ep-2, Bp-3 and Es-1 by stimulating the mantle surface of the animal with brush strokes (Fig. 5).5.It was suggested that sensory inputs which inhibited the photoexcitive neurones were derived from some mechanoreceptors other than tactile receptors within the mantle (Fig. 6).6.A stereotyped response (the mantle-levating reflex) was evoked by tactile stimuli given to the mantle surface. This response could also be elicited by direct electrical stimulation of the photoexcitive neurones (Fig. 8).7.The photoexcitive neurones played a role in regulating the transmission of the tactile sensory information (Fig. 9).8.From these results, it was postulated that the photoexcitive neurones modified the activity level of the mantle-levating reflex.