. The Biological bulletin. Biology; Zoology; Marine biology. 330 SVEN HORSTADIUS H. Isolation of ani + an2 + vegi Only three fragments of this type were studied, but they all devel- oped in a similar way. They formed, much as the isolated four animal cells of the 8-cell stage, a blastula with an apical organ and a ciliated band (Fig. 8, B, C). Thus no real deep gastrulation took place, although the vegetative end of the larva at one stage may be a little curved inwards, as in a normal larva just at the beginning of the gastrulation. This part later differentiated into an epithelium which mostl
. The Biological bulletin. Biology; Zoology; Marine biology. 330 SVEN HORSTADIUS H. Isolation of ani + an2 + vegi Only three fragments of this type were studied, but they all devel- oped in a similar way. They formed, much as the isolated four animal cells of the 8-cell stage, a blastula with an apical organ and a ciliated band (Fig. 8, B, C). Thus no real deep gastrulation took place, although the vegetative end of the larva at one stage may be a little curved inwards, as in a normal larva just at the beginning of the gastrulation. This part later differentiated into an epithelium which mostly looked like ectoderm, but perhaps was a little more densely ciliated. In the larva from the upper quartet of the 8-cell stage the "ciliated band" rather was a ciliated field of high cells, occupying the lower part of the larva (Fig. 5). Our present larvae differ in the respect that we here have a real band, surrounding the ectoderm-like area just mentioned, which in turn must correspond to the-inside of the lappets and the oesophagus. In one of the larvae this area first curved inwards and was later turned out again (Fig. 8, B), whereas in the other two it remained as a very shallow invagination; the ectoderm formed like a lappet on one side (Fig. 8, C). Thus also a larva from which veg2 has been removed seems to develop in accordance with the prospective significance of the material. I. Isolation of an^ + vegi The same holds for the fragments an2 + vegi. A great many larvae disappeared. The 9 surviving ones differentiated, although varying in shape, into blastulae with a broad, ciliated band around the equator (Fig. 9). As the ectoderm does not expand, the ciliated band. A BCD Fig. 9. Larvae from the two middle layers of the 16-cell stage: an2 + vegi. is very thick and broad. The pretrochal, animal epithelium which corresponds to the thin ectoderm formed by an2 is generally thinner than the vegetative epithelium of the band (corresponding to the inside of the lappe
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