. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 4. Expression of engrailed in the pleonic nerve cord of the first postembryonic stage (PO I): pgl. first pleonic ganglion: pg4, fourth pleonic ganglion; pg5. fifth pleonic ganglion; tg. terminal ganglion. (A) The six ganglia of the pleon of the first stage after hatching (PO I) (ventral aspect). (B) Higher magnification of the same preparation, showing the ganglia of the fourth and fifth pleomeres. They exhibit a serially repeated pattern of two areas of engrailed expression. An anterior region of cells (neurons, glia
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 4. Expression of engrailed in the pleonic nerve cord of the first postembryonic stage (PO I): pgl. first pleonic ganglion: pg4, fourth pleonic ganglion; pg5. fifth pleonic ganglion; tg. terminal ganglion. (A) The six ganglia of the pleon of the first stage after hatching (PO I) (ventral aspect). (B) Higher magnification of the same preparation, showing the ganglia of the fourth and fifth pleomeres. They exhibit a serially repeated pattern of two areas of engrailed expression. An anterior region of cells (neurons, glia, or their precursors) with relatively small nuclei (asterisks) and a posterior region with large engrailed-positive cells (arrows). (C) The terminal ganglion (same preparation as in (A)). The pattern of engrailed expression reveals the composed nature of this ganglion. The asterisks indicate the anterior segmental engrailed area and the arrows point to the posterior segmental engrailed area (compare Fig. 4B). The pattern of engrailed expression in the seventh ganglion anlage (7) is somewhat reduced when compared with that of the sixth ganglion an- lage (6). and that disappears during further development. From the outset, the morphological border between the ter- minal segment and the telson lies behind the sixth pleonic engrailed stripe. Phylogemtic significance of pleonic engrailed stripes eight and nine The eighth and ninth pleonic engrailed stripes are also considered to indicate vestigial segments that recapitulate ancestral conditions. This suggestion is based on the sim- ilar appearance of stripes seven to nine and on the fact that many non-malacostracan crustaceans possess more segments than malacostracans. However, it is difficult to say how far back stripes eight and nine point in phylogeny and in which ancestral lineage these segments have been lost in the adults. The question of whether segmentation and tagmatization of the Malacostraca are primitive or are derived
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
