Figure 2.

A. Diagram of the left side of the brain of Astacus leptodactylus, seen from the ventral side and showing the disposition of the deutocerebral organ first described by Bazin (1969a, b). This organ consists of a central cluster of cells that surround a homogeneously staining cavity. The central cluster of cells are connected by thin strands of fibers that run laterally over the surface of the accessory lobe to end amongst the projection neurons in Cluster 10 and medially around the nerve root of the nerve from the antennule to end in the local olfactory neurons in Cluster 9. B. Light micrograph of a section through the cavity in the center of the deutocerebral organ cell cluster of A. leptodactylus showing the amorphous contents and the surrounding cells with characteristically dark granules in their nuclei. C. Electron micrograph of a section through the same area as in B of A. leptodactylus which shows the membranes of the cells surrounding the cavity to be sculpted into many finger like processes that contact the structureless contents. D. Light micrograph of a semi-thin, toluidine blue stained section through the neurogenic niche of Procambarus clarkii. The components of the neurogenic system of P. clarkii, with a central niche consisting of a cluster of cells surrounding a central cavity and linked by fiber strands to the local and projection olfactory neurons, is homologous with the deutocerebral organ of Astacus. Abbreviations: amas cellulaire, A. C.; groupe olfactif antérieur, CEL.OLF.ANT; groupe olfactif postérieur, CEL.OLF.POST.; glomérule olfactif, GLOM.OLF; tractus antérieur, T. A.; tractus postérieur, T. P.; terminal bar, BT; Cluster 9, CL9; Cluster 10, CL10; nucleus, N; substance in the cavity, S; villi, V; vascular cavity, VC. Scale bars: B, 20 μm; C, 15 μm; D, 20 μm. (A, from Bazin, 1969a; B and C are previously unpublished images from Bazin, 1969b; D from Zhang et al., 2009)