Contribution à l'étude du système nerveux, des glandes annexes et des cellules neurosécrétrices de Hemilepistus reaumurii (Audouin, 1826) (Isopode, Oniscoïde) (Contribution to the Study of the Nervous System, the Accessory Glands, and the Neurosecretory Cells of Hemilepistus reaumurii (Audouin, 1826) (Isopoda, Oniscidea))

The present paper investigates the nervous system and neurosecretory centres of the terrestrial isopod, Hemilepistus reaumurii by means of light microscopy. A descriptive anatomical and histological study has allowed us to identify a classical organization, which comprises the brain, the sub-oesophageal mass, and the ventral nervous chain. The brain is composed of the protocerebrum that continues in the poorly developed optic lobes, each of which contains a medulla interna, a medulla externa, and a lamina ganglionaris. The deutocerebrum is vestigial and the tritocerebrum is linked to the sub-oesophageal mass by the perioesophageal ring. The ventral nervous chain is made up of seven pairs of thoracic ganglia and six pairs of poorly separated abdominal ganglia. The neurohemal organs comprise the sinus glands and the cephalic lateral nerve plexus. The glands that are connected to the nervous system are the antennary glands and the Y-organ. The sinus gland is opalescent and has the shape of a cul-de-sac; it is situated to the ventral side of the optic lobe at the level of the lamina ganglionaris. It has no connection with the Y-organ, but it seems to be connected to the protocerebral neurosecretory cells. The moulting organ (Y-organ) seems to go through a period of rest during the cold season (November to February), when the animals remain in the soil and are not moulting: a resting period for the secretory cells. The antennary glands are situated at the bases of the antennae; they look well developed and their cells are in a state of mitotic activity. As for the neurosecretory cells, we have observed the presence of four main types of cells, here referred to as: A, B, β, and δ, after Matsumoto (1959) and Martin (1981). These show variations in their number, size, and distribution. /// Ce présent travail est une investigation, à l'aide de la microscopie optique, du système nerveux et des centres neurosécréteurs chez l'isopode terrestre Hemilepistus reaumurii. L'étude descriptive anatomique et histologique nous a permis d'identifier une organisation classique qui comporte le cerveau, la masse sous-œsophagienne et la chaîne nerveuse ventrale. Le cerveau comprend: le protocérébron, qui se prolonge latéralement par les lobes optiques, peu développés, formé chacun par une medulla externa, une medulla interna et une lamina ganglionaris; le deutocérébron rudimentaire et le tritocérébron, connecté à la masse sous-œsophagienne par le collier péri-œsophagien. La chaîne