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The morphology of the larval and adult brain of Philosamia ricini , and changes during pupal period have been described. In the larva, each mushroom body has 2 calyces, a stalk with a feebly developed outer and a well-developed inner root, the latter extending posterolaterally to the central body, and joined with each other. The elongated central body has fibrous connectoins with the deutocerebrum. Optic commissures join the 3 laterally situated optic ganglia. The corpora ventralia are joined with each other by a paired ventral commissure (single in adult). Antennal nerves arise from the posteroventrally situated deutocerebral lobes, and the antennal commissure joins the 2 opposite lobes. The small, paired, glomerular tritocerebrum is placed posteroventrally to the deutocerebrum, and fibres from these travel to the crura cerebri. During metamorphosis, apart from general increase in size, changes are observed in the mushroom body, central complex, optic ganglia and deutocerebrum. In addition, certain structures such as the antennal cortex, ellipsoid body and chiasmata between optic ganglia are also observed. In the adult, behind the well-developed central body, is an ellipsoid body. The swollen pons cerebralis joins the 2 protocerebral lobes. The medulla interna is divided into 2 smaller lobes, and the deutocerebral lobes are differentiated into cortical and medullary zones.

The corpora pedunculata, or mushroom bodies, are paired lobes of neuropile present in the protocerebrum or dorsal brain of all insects. They are divisible into three parts: calyx, stalk and roots. The latter usually comprise two simple lobes, the a and ft lobes. The corpora pedunculata of a variety of Lepidoptera were examined. All had a double calyx-cup. Each ‘cup-cavity’ is composed of ‘globuli’ cell bodies. The broad stalk, a tract of fibres and neuropile, leads from the calyx to the complex ‘roots’—a, g and y lobes. A third group of globuli cells near the calyx gives rise to a tract leading to a second lobe-system—the tripartite Y-lobe—in the roots. As neither the Y tract nor the Y lobe has been described before in any insect, their possible homologues are unknown. The two lobe systems in the roots are closely intertwined, yet have no interaction except in the y lobe. A number of different neuron types with branches in the mushroom bodies has been described from Golgi preparations. Some (intrinsic cells) divide in the calyx and again in the roots, but do not pass out of the mushroom bodies. Others (extrinsic cells) branch in the mushroom bodies and in other areas of the brain, thus connecting two regions. Intrinsic cells arise from cell bodies in the calyx-cups or posterior to them. There are two types: one has extensive spine-covered branches in the calyx, while the second has claw-like terminals covering a narrow cylindrical field. Processes from these cells run to the a, j>and y lobes via the stalk. A wide-field accessory cell, which arises from the third group of globuli cell bodies, also has claw-like endings in the calyx. A process of this cell runs in the Y-tract to the Y-lobe. Extrinsic terminals in the calyx arise from cells branching in the antennal lobe, in an accessory optic area in the protocerebrum, in the ‘undifferentiated’ protocerebral neuropile, or in the suboesophageal lobes. The antennal terminals in the calyx are knob-like. It is proposed that they form the centre of the ‘glomeruli’ typically present in calycal neuropile. The claws of the bunched intrinsic and accessory cells probably fit around these knobs. Within the stalk, different subvarieties of intrinsic cells have been distinguished on the basis of the distribution of the side-branches and spines which they bear. The stalk is thought to be the site of extensive postsynaptic interaction between intrinsic cells. Fibres in the stalk run in bundles or groups. All the fibres in one bundle are of the same subvariety. In the roots, the subvarieties of intrinsic cells have different branching patterns. The a and B lobes are not homogeneous, but are divided into sublobes. Extrinsic fibres ramify only within one sublobe generally, though some have very large fields. The connexions of the roots are obscure. Some extrinsic fibres branch again in the ‘undifferentiated’ protocerebral neuropile; others, from the B lobe, may run to the suboesophageal lobes. There are profound differences between the internal organization of the mushroom bodies in Hymenoptera (Kenyon 1896; Goll 1967) and Lepidoptera. The functional implications of the Lepidopteran form are discussed.

The histochemical localization of cholinesterase in the cockroach (Periplaneta americana) brain was investigated and compared to the localization of catecholamines as described by others. An inverse relationship occurs in many areas. The calyx, negative after catecholamine staining, stains with cholinesterase in its ventral two-thirds. The alpha and beta lobes appear striped after catecholamine staining and are unstained by cholinesterase. Neuronal cell groups stained by catecholamines are unstained by cholinesterase. A few cells of the pars intercerebralis are stained by cholinesterase, but not by catecholamines. Neuropiles in all lobes of the brain are stained intensely by cholinesterase, while only a few fibers in these areas are seen after catecholamine procedures. The medulla of the optic lobe, unstained by catecholamines, is stained intensely by cholinesterase. An external semilunar zone of the lobula of the optic lobe is stained intensely by cholinesterase and after catecholamine procedures. Neither transmitter can be found in the globuli cells, the dorsal one-third of the calyx, the stem of the mushroom body, and between the catecholaminergic stripes of the alpha and beta lobes. Both transmitters can be found in parts of the central body.

Une etude histologique de la region posterieure du protocerebron (calices des corps pedoncules), realisee, au cours des dernieres phases du developpement, chez une Fourmi primitive (Mesoponera caffraria, sous-famille des Ponerinae), a mis en evidence, au niveau des cellules globuleuses, l'existence de deux groupes de cellules qui different par la taille et l'activite mitotique. Cette dualite se maintient durant plusieurs etapes de l'ontogenese jusqu'a un stade avance de la periode nymphale.

The aim of this study was to investigate possible relationships within the worker population of a single red wood ant nest (Formica rufa), between measures of size and measures of terrestrial foraging efficiency. Significant correlations were found, for a sample of 45 workers from this nest, between efficiency of navigation through a complex maze, and the size of the head and of certain component nervous and sensory structures. The component structures were of two types: the external sensory receptor areas, and the calyces of the corpora pedunculata (mushroom bodies) of the brain. Correlations with efficiency for other size measures from brain structures and from a leg were not significant. Possible bases for the size-efficiency relationships were discussed, in terms of the factors known to influence size and foraging behavior in wood ants.

The neuropile of the mushroom bodies is enveloped by a glial coating, sending a few septa inside. It is formed of nerve fibres and nerve endings which are smaller, more uniform in size, and more regularly arranged than those of the surrounding neuropile. The nerve endings are full of clear vesicles, dense granules 600–1100 A in diameter, and mitochondria; the nerve fibres contain neurotubules, mitochondria, and often also some vesicles and granules. The fibres mainly follow a parallel trend; where the endings are present, they intermingle with the fibres without any recognizable order. The nerve fibres and endings come into contact with each other without glial sheets separating them; the cleft is 100–200 A wide; no structural character was observed indicating the areas where synapses occur. The functional polarity of the contacts, the origin of the fibres, and the nature of the dense granules are discussed.

A technique is described for training ants in a T-maze, using olfactory cues. True olfactory learning occurs and amputation of the antennae prevents the use of olfactory cues. Amputation of one antenna causes a slight falling off in performance, but the ants still perform well above chance level after the operation. After ants have been trained in an olfactory discrimination, the effect of brain lesions on performance is studied. Severing the tracts between both antennal lobes and the alpha lobes of the mushroom bodies causes performance to fall back to chance level. Severing the tracts on only one side of the brain, or lesions placed elsewhere, does not disturb performance. Results are discussed in relation to the involvement of the mushroom bodies and antennal lobes in learning. (Author)

Aristotle (in De Anima) supposed the mind of insects was located between the head and abdomen, and was sometimes multiple, which explained why an insect continued to live when cut in two. The behavioural autonomy of the headless insect is illustrated in recent experimental studies. Gryllus campestris can be made to sing calling and courtship songs on stimulation of the thoracic connectives (Otto 1971); a male mantid can complete a sequence of mating behaviour with its head eaten away (Roeder 1963) and a Hyalophora cecropia pupa, without a brain, can undergo a sequence of activities enabling it to escape from the cocoon (Truman 1971).

Discharges of the olfactory units in the brain of the honey-bee were recorded extracellularly. Discharges were excitatory and inhibitory and showed on and on-off responses. In the on responses, phasic, phasic-tonic, and tonic patterns were found. No relation between discharge pattern and the region in the brain was found. The dominant pattern was phasic-tonic in the excitatory and tonic in the inhibitory units. Rebound or long-lasting phenomena seemed to be one of the characteristics of the neurones in the central nervous system. The latency of the response showed that olfactory information entering the deutocerebrum from the antenna was carried to the calyx of the ipsilateral brain via the antenno-cerebral tracts reported by Kenyon (1896), and then to the protocerebral lobe through the stalk of the mushroom body. The information was also carried to the contralateral brain after passing through the calyx of the ipsilateral brain or the central commissure.

Electrical activity in response to light stimuli was recorded from the brain of the cricket (Gryllus domesticus) using stainless steel microelectrodes. Four basic types of elements were observed as follows: (1) units which registered ambient light intensity by frequency of firing as well as responding with transient changes in rate to stepwise increases or decreases in intensity; (2) units which fired at a higher frequency in dark than in light; (3) units which fired continuously at low level in light and responded with a transient high frequency burst to light off; and (4) units which responded with a brief burst to on and off, but tended to be “on-dominant” or “off-dominant.” Also observed were synchronized spikes in mushroom body responding primarily to light off, but also on occasion to light on, and often accompanied by single unit responses. The units registering intensity are probably homologous with units showing similar properties recorded from the visual systems of several other arthropods and usually referred to as “sustaining units.” On-off, off, and dark units are also known from other forms. The mushroom body light responses were similar to synchronized spikes recorded in cockroach mushroom body following antennal stimulation.

One of the major evolutionary trends in the Insecta has resulted in the increase and size and complexity of the mushroom bodies (corpora pedunculata) in the brains of social hymenoptera. Since ants and bees are known to learn well, it seems reasonable to suppose that these lobes are involved. In a previous study (Vowles, 1964a) it was shown that, in wood ants which had been trained in an olfactory task, lesions within the mushroom bodies did not disrupt performance, but severing tracts between the antennal lobes and the alpha lobes (Vowles, 1955) of the mushroom bodies caused failure to recognize the olfactory cues. Unilateral lesions disrupted performance only if the contralateral antenna had been amputated.