Entomology : with special reference to its biological and economic aspects . f egg of a beetle, Clytra Icrxiiiscula. h, blastoderm; g, germband; y, yolk granule; yc, yolk cell.—After Lec.\illon. substances the qualities of the two parents are combined in theoffspring. Needless to say, the minute details of the processof fertilization are of the highest biological importance. Blastoderm.—Tn an arthropod ovum the yolk occupies acentral position {centrolecithal type), Ijeing enclosed in a thinlayer of protoplasm. From the segmentation nucleus justmentioned are derived many nuclei, some of which m
Entomology : with special reference to its biological and economic aspects . f egg of a beetle, Clytra Icrxiiiscula. h, blastoderm; g, germband; y, yolk granule; yc, yolk cell.—After Lec.\illon. substances the qualities of the two parents are combined in theoffspring. Needless to say, the minute details of the processof fertilization are of the highest biological importance. Blastoderm.—Tn an arthropod ovum the yolk occupies acentral position {centrolecithal type), Ijeing enclosed in a thinlayer of protoplasm. From the segmentation nucleus justmentioned are derived many nuclei, some of which migrateoutward with their attendant protoplasm to form with theoriginal peripheral protoplasm a continuous cellular layer, theblastoderm (Fig. i88). 148 ENTOMOLOGY Germ Band.—The blastoderm, at first of uniform thick-ness, becomes thicker in one region, by cell multiplication,forming the genu baud (priniitivc streak, etc.) ; this appearsin surface view as an oval or elongate area, denser than theremaining blastoderm, with which it is. of course, continuous. Fig. Transverse section of germ band of Clytra at gastrulation. g,laver.—After Lecaillon. ;rm band; i, inner Gastrulation.—The germ band next infolds along the me-dian line, appearing, in cross section, as in Fig. 189; thetwo lips of the median groove, close together over the inva-ginated portion and form an outer layer, or ectoderm (), while the in^?aginated portion spreads out as an inner Fig. 190.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectentomology, bookyear1
