. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 362 L. R. PAGE. 29 Figure 28. Frontal section through larva at mantle fold hypertrophy stage showing merger of right and left limbs of visceral loop (R and L, respectively) adjacent to intestine (I). MG = mantle gland; VG = visceral ganglion; VP = visceral placode. Scale, 5 //m. Figure 29. Slightly deeper section showing visceral nerve (arrows) extending around distal intestine (1) from visceral ganglion (VG) towards visceral placode. Scale, 5 tim. Figure 30. Visceral nerve (arrow) within base of visceral placode (VP). I = i
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 362 L. R. PAGE. 29 Figure 28. Frontal section through larva at mantle fold hypertrophy stage showing merger of right and left limbs of visceral loop (R and L, respectively) adjacent to intestine (I). MG = mantle gland; VG = visceral ganglion; VP = visceral placode. Scale, 5 //m. Figure 29. Slightly deeper section showing visceral nerve (arrows) extending around distal intestine (1) from visceral ganglion (VG) towards visceral placode. Scale, 5 tim. Figure 30. Visceral nerve (arrow) within base of visceral placode (VP). I = intestine. Scale. I ^m. on Melibc and Lyninaea stagnalis (Regondaud, 1961. 1964) show that visceral loop ganglia differentiate from torted visceropallial ectoderm, as they do in prosobranchs. Nevertheless, the concept of visceral loop shortening as the cause of euthyneury is popular (see Fretter and Gra- ham, 1962; Bulloch, 1965). It might be envisioned that visceral loop ganglia become concentrated against the ce- rebral ganglia of their respective pre-torsional sides as threaded beads pushed together during shortening of a convoluted string. However, as pointed out previously by Regondaud (1961) for Lymnaea. and also seen in Melibc and Aplysia califomica (Kriegstein, 1977a, b), all visceral loop ganglia differentiate within close proximity along a short visceral loop. This loop simply remains short in cephalized species, while the rest of the body elongates after metamorphosis. Instructions to elongate are given instead to peripheral nerves. This is more than a semantic point if cephalization is to provide a mechanism for eu-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marine Biological Laboratory (Woods Hole, Mass. ); Marine Biological Laboratory (Woods Hole, Mass. ). Annual report 1907/08-1952; Lilli
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
