. Annals of the New York Academy of Sciences. Science. CELL-LTNEAGE. thus formed some of the small cells usually extend, appearing in sections in the sharpest contrast both to the large rounded mesoblast-cells and to those of the lateral ectoblast (Fig. 3, C\ From this point the mesoblast-bands extend towards the sides and ultimately curve upwards (forwards with respect to the adult long axis) at the sides of the embryo.^. A B Fig. 2. Corresponding surface views, from the lower pole, of early embryos oi Avici a (A) and A'ereis {B) ; the limit of the ectoblast, i. c, the lip of the blastospore,
. Annals of the New York Academy of Sciences. Science. CELL-LTNEAGE. thus formed some of the small cells usually extend, appearing in sections in the sharpest contrast both to the large rounded mesoblast-cells and to those of the lateral ectoblast (Fig. 3, C\ From this point the mesoblast-bands extend towards the sides and ultimately curve upwards (forwards with respect to the adult long axis) at the sides of the embryo.^. A B Fig. 2. Corresponding surface views, from the lower pole, of early embryos oi Avici a (A) and A'ereis {B) ; the limit of the ectoblast, i. c, the lip of the blastospore, is shown by the heavy line. A shows the single pair of vestigial entoblasts (e, e) of Aricia lying in front of the primary mesoblasts which are dividing to fonn the mesoblast-bands (cf. Fig. i, C, which shows the same specimen in sagittal section). B shows two pairs of superficial entoblasts, lying behind the macro- mere D, and the spindles of a deeper budding of the " primary mesoblasts" (cf. Fig. 3, A, for section of this stage). A, B, C, D, the four basal entoblasts or macromeres; a^-c^, the fourth quartet of " micromeres " (entomeres); a^-d^, the fifth quartet (entomeres) ; c'^-d^, deriva- tives of the third quartet (ectomeres); M, J/, the primary mesoblasts (shaded in B). Up to this point the account here given is substantially the same as that contained in my earlier paper on Nereis. Regard- iJn Aricia the mesoblast-bands are foraied much earlier, while the primaiy meso- blasts still lie at the surface (Fig. i, C) ; and they lie at first side by side, nearly parallel to each other, extending upwards behind the entoblast-plate (Fig. 7). In both these respects Aricia is somewhat similar to Lunibriciis (Cf. \Vilson, Embry- ology of the Earthworm, Fig. 30 : Joiirn. Morph., 1889).. 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
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1877
