The size of the germ anlage varies relative to the length of the egg. In nearly all species, the nuclei arrive at the periphery to form a blastoderm that encompasses the whole surface of the egg. In metamorphic species, such as fruit flies and honey bees, the germ anlage forms from nearly the entire blastoderm surface. However, in direct developing species (such as the grasshopper and cricket), after the formation of a uniform synctyial blastoderm, nuclei migrate and aggregate near the posterior pole, where the germ anlage forms. The germ anlage thus forms from a relatively small proportion of the blastoderm. In the former case, called long-germ-type embryos, the complete body pattern (head, gnathal, thoracic, and abdominal segments) is patterned at the blastoderm stage and all segments appear nearly simultaneously in development. In contrast, in short-germ-type embryos, the head lobes, the most anterior trunk segments, and the posterior terminus are patterned first. Additional segments are added progressively, through proliferative growth. Some insects develop with germ types intermediate between these two extremes. The pleisiomorphic condition for insects is believed to be an intermediate-sized germ anlage. Short/intermediate germ embryogenesis is predominant in direct-developing hemimetabolous insects; more derived, metamorphic insects exhibit long-germ development. However, this division is not clear-cut. In some insect families, closely related species can exhibit both short- and long-germ types of development.
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