origin of ganglia circumblastoporal nerve cord, incl. posterior part of brain ectoderm ectoderm ectoderm, proctodaeum, ectomesoderm ectoderm, proctodaeum, ectomesoderm mesoderm, endoderm endoderm circumblastoporal nerve cord, incl. posterior part of brain
Figure 21.2 Cell lineage of an annelid as represented by Podarke (based on Treadwell 1901). Blastomeres of the episphere are in the light grey areas. The grey tones and the two types of cross-hatching correspond to similar areas in Figures 21.1, 21.3 and 21.4. The origin of different parts of the central nervous system is indicated (see text). It might be expected that descendants of the cells 2a-c contribute to the ventral nervous system, but this has not been investigated.
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