. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HADDOCK SWIMBLADDER DEVELOPMENT 181 The mesenchymal cells had disappeared from the duct wall, leaving only a chaotic syncytial epithelium. j collected specimens Collected larvae were obtained from the Bureau of Commercial Fisheries and from seining by the author. Larvae in the first category measured mm while in the second group four averaged mm and one measured mm in total length. Major features of swimbladder development in these specimens were cavity expansion, increasing antero-ventral localization of most
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HADDOCK SWIMBLADDER DEVELOPMENT 181 The mesenchymal cells had disappeared from the duct wall, leaving only a chaotic syncytial epithelium. j collected specimens Collected larvae were obtained from the Bureau of Commercial Fisheries and from seining by the author. Larvae in the first category measured mm while in the second group four averaged mm and one measured mm in total length. Major features of swimbladder development in these specimens were cavity expansion, increasing antero-ventral localization of most of the cuboidal ( ?gland- ular) epithelium, rete development, and the appearance of accessory tissue layers. Swimbladder development was arbitrarily divided into three stages on the basis of larval size; vis. 4-5 mm, 5-10 mm, and mm. In laboratory-reared larvae of 4-5 mm the cavity was small and the lining deeply folded. In collected specimens of similar length the cavity was noticeably larger and the folds not as deep. Cuboidal epithelium surrounded the cavity, as did rete vessels, except most postero-dorsally where a small area was lined by thin squamous epithelium. Occasionally vacuoles were evident within the cuboidal liv FIGURE 2. Cross-section through swimbladder region of a day 16-17 embryo. Abbreviations are: pd = pneumatic duct, pp = pigmented peritoneum; X 156. In 5-10-mm collected larvae the cavity was still further expanded. The swimbladder appeared teardrop-shaped in lateral view, tapering posteriorly. The trunk of the rete ran along the outside of the ventral swimbladder wall and divided in two before entering the cavity anteriorly. Its vessels were most abundant here, but it also sent branches caudally along the lateral walls of the bladder. This organization apparently determined the localization of the cuboidal epithelium, which had proliferated over the anterior and antero-ventral walls of the bladder and in some specimens covered a small port
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