. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 184 ANNALS OF THE SOUTH AFRICAN MUSEUM hairs o^ J. lalandii, but in a position corresponding to that of the group hairs of Carcinus maenas there is an obvious antero-dorsal field (fig, 68) with numerous comparatively stout, medium-sized hairs, each of which (fig. 69) is jointed, heavily fringed at the tip, and directed towards the aperture. In the statocyst of other species Farre (1843) and Panning (1924) have also indicated that there is a triangular field of sensory hairs guarding the aperture. Alt
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 184 ANNALS OF THE SOUTH AFRICAN MUSEUM hairs o^ J. lalandii, but in a position corresponding to that of the group hairs of Carcinus maenas there is an obvious antero-dorsal field (fig, 68) with numerous comparatively stout, medium-sized hairs, each of which (fig. 69) is jointed, heavily fringed at the tip, and directed towards the aperture. In the statocyst of other species Farre (1843) and Panning (1924) have also indicated that there is a triangular field of sensory hairs guarding the aperture. Although their function has not yet been determined, Prentiss (1901) suggested that the group hairs of Carcinus might be modified tactile hairs that had been invaginated during the formation of the statocyst. 3. EYES The main visual organs of adult decapod Crustacea are a pair of stalked, lateral, compound eyes, but in some species a small unpaired or median eye, which is characteristic of malacostracan larvae, may be retained in the adult, (a) Median eye According to Gilchrist (1913^), a median eye-spot, as well as lateral compound eyes, occurs in the recently-hatched naupliosoma larva of J^. lalandii, and Von Bonde (1936) has indicated that it is a feature of an even younger prenaupliosoma stage but that 'it disappears and is lost' (p. 18) after the 3-8 mm stage of the phyllosoma larva. However, in the course of the present study close inspection of the phyllosoma and puerulus stages proves that the small median eye is still visible through the transparent exoskeleton; moreover, it also persists in the adult. It projects mid-dorsally from the brain immediately below the fused eyestalks of the compound eyes and, on exposure of the anterior part of the nervous system of juvenile and more mature specimens (fig. 61), it is easily detected by its mass of reddish pigment. In sections of the puerulus stage (fig. 70) the bulk of the pigment is seen to be arranged in two crescentic layer
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
