. C D Text-fig. 33. Diagrammatic reconstructions of four stages (a-d) in the fatty investment of a regressing larval swimbladder in Cyclothone livida. The gas-gland is shown black, ft, fatty investment of swimbladder; lu, lumen of swimbladder;/)/), pig- mented peritoneum; rsb, regressed swimbladder; sbw, swimbladder wall. Above and below the vertical diameter of the sphere, there was only a thin covering of fat. Finally, in a 56-mm. individual the remnants of the larval swimbladder measured no more than 0-15 mm. in diameter and needed to be carefully looked for in its fatty investment. It woul
. C D Text-fig. 33. Diagrammatic reconstructions of four stages (a-d) in the fatty investment of a regressing larval swimbladder in Cyclothone livida. The gas-gland is shown black, ft, fatty investment of swimbladder; lu, lumen of swimbladder;/)/), pig- mented peritoneum; rsb, regressed swimbladder; sbw, swimbladder wall. Above and below the vertical diameter of the sphere, there was only a thin covering of fat. Finally, in a 56-mm. individual the remnants of the larval swimbladder measured no more than 0-15 mm. in diameter and needed to be carefully looked for in its fatty investment. It would thus appear that the swimbladder is fully adipose in adults of about 35 mm. and upwards. In Cyclothone livida (also from St. 3094) the sequence of changes is much the same and is sum- marized in Text-fig. 33. As in C. braueri, the larval swimbladder was completely regressed and surrounded by a sausage-shaped mass of fat when the fish had reached a length of about 37 mm. This most advanced stage in the development was examined microscopically. In Text-fig. 34 is a drawing of a transverse section at the level of the regressed swimbladder (see also PI. I, fig. 2). The left-hand figure shows the reticular system of fat-storing cells surrounding the central regressed part of the larval swimbladder. This part is shown enlarged on the right. An outer fibrous layer encloses a mass of regressed gas-gland cells, mostly without nuclei, and the remnants of the retial capillaries. The remaining space is filled up with fine loosely-woven reticular tissue, which is undoubtedly the remains of the submucosa. The tunica externa must be represented by the outer fibrous layer, which has much the appearance of the outer circular layer fibres described by Nusbaum-Hilarowicz (1920). The mass of fat-charged cells is almost entirely bounded by the darkly pigmented peritoneum with its fine mosaic of melanophores. Thus the fat is deposited between the peritoneum and the tunica externa and in this way c
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