. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. 70 EMBRYOLOGY OF INSECTS AND MYRIAPODS Scolopendra, Polydesmus, Phyllodrumia, and Gryllotalpa (Heymons, Nus- baum, and Fulinski) and Eutermes (Knower). Philiptschenko preferred to speak of an upper, or outer (ectoderm), and an inner, or lower, layer, believing that a sharp line cannot be drawn from the further derivatives of the inner layer, , secondary (entoderm and mesoderm) layers. He contended that
. Embryology of insects and myriapods; the developmental history of insects, centipedes, and millepedes from egg desposition [!] to hatching. Embryology -- Insects; Embryology -- Myriapoda. 70 EMBRYOLOGY OF INSECTS AND MYRIAPODS Scolopendra, Polydesmus, Phyllodrumia, and Gryllotalpa (Heymons, Nus- baum, and Fulinski) and Eutermes (Knower). Philiptschenko preferred to speak of an upper, or outer (ectoderm), and an inner, or lower, layer, believing that a sharp line cannot be drawn from the further derivatives of the inner layer, , secondary (entoderm and mesoderm) layers. He contended that in Isotoma the unpaired median part of the inner layer is a mixed one, giving rise to both entoderm and mesoderm. Thus far the ectoderm is accounted for. The question of the deriva- tion of entoderm and mesoderm now arises. In descriptive embryology of arthropods we are confronted with the difficulty of a terminology in. Fig. 42.—Germ disk of Peripatopsis. {.an) Anus, {bp) Blastopore, (m) Mouth. {From Snodgrass after Balfour.) which one group of writers uses the term "entoderm" for one of the two components of the inner (lower) layer while another group uses it for the yolk cells. Prior to the time of the appearance of a paper by Grassi (1884) nearly all investigators of insect embryology were divided into two groups; either they followed Dohrn (1866) in deriving the mid-gut epithelium from the yolk cells, or they followed Kowalewsky in deriving it from the inner wall (splanchnic layer) of the mesodermic somites. In 1884 Grassi demonstrated the bipolar origin of the mid-gut epithelium from the inner (lower) layer in the honeybee. This was followed by a brief paper of Kowalewsky (1886) in which he devised a theory wherein he regarded the insect egg at the time of the formation of the germ layers as comparable to a gastrula so stretched out that the mid-gut epithelial rudiment (mesenteron or entoderm) was pulled into two halves. The stretching of the gastrula resulted
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