. Bulletin of the British Museum (Natural History). i8 E. TREWAVAS cannot confirm by examination with a dissecting microscope for either the boot- shaped or the sessile pad, and Thys gave no evidence for his statement. Dissection of both the hanging and the sessile pads reveals only connective tissue inside, often fat-laden. In the midst of this is a lamina of cartilage and bone that is an expansion of the anterior edge of the second epibranchial (fig. ii). On the oral side the mem- brane is raised into ridges and bosses bearing sensory cells. The histology of these pads has been little studie
. Bulletin of the British Museum (Natural History). i8 E. TREWAVAS cannot confirm by examination with a dissecting microscope for either the boot- shaped or the sessile pad, and Thys gave no evidence for his statement. Dissection of both the hanging and the sessile pads reveals only connective tissue inside, often fat-laden. In the midst of this is a lamina of cartilage and bone that is an expansion of the anterior edge of the second epibranchial (fig. ii). On the oral side the mem- brane is raised into ridges and bosses bearing sensory cells. The histology of these pads has been little studied. Al Hussaini & Kholy (1954) found in the pharynx of Tilapia nilotica columnar cells interspersed with granular cells. Stolk (1957) described secretory cells in the pads of female Haplochrmis multicolor with- out comparing them with the males. Fishelson (1956 : 588, fig. 19) demonstrated both glandular and sensory cells in Tilapia thoUoni not only between and beside the upper pharygeal tooth-plates, but also on the floor of the pharynx, including the gill-arches. MacroscopicaUy the pad is very similar in Pelmatochromis and Tilapia, but between Tilapia on the one hand and two of the species of Pelmatochromis (and Ft. congictis) on the other there is a difference in the epibranchial structures. In these [P. huettikoferi and P. nigrofasciaius) as also in Chromidotilapia, there is a long series of slender epibranchial gill-rakers on the first arch and the fold of skin (frenum) at the hinge between suspensorium and epibranchial is remote from the epi-ceratobranchial joint. This leaves a free passage for a current, respiratory or food-bearing, to pass between the pharynx and the upper part of the parabranchial chamber, in which direction can only be tested by experiment (fig. 12A). In Tilapia, on the other hand, the epibranchial gill-rakers are few, short and blunt and the frenum is attached near the epi-ceratobranchial joint. The upper gill-filaments are attached along a line t
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