Inhibitors of DNA synthesis change the differentiation of body segments and increase the segment number in horseshoe crab embryos (Chelicerata, Arthropoda)

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Abstract
The inhibitors of DNA synthesis change the differentiation of abdominal segments of the horseshoe crab and increase the number of segments in 90%–100% of the surviving embryos. The data suggest the following: The primordia of segments are formed one by one from the cells at the posterior end of the embryonic area, and they are determined soon after formation. When DNA synthesis inhibitors are applied, the forming primordium acquires a character intermediate between the anterior segment already determined and the segment next to be determined. The abnormal differentiation is possibly caused by a time lag between DNA synthesis and the rest of metabolism. The specific character of each segment of normal embryos and malformations successively determines that of the next segment. By this route the whole number of segments is established.