Segmentation of the central nervous system in ligated embryos ofDrosophila melanogaster

We have visualized segmentation in theDrosophila embryoniccentral nervous system (CNS) by staining for acetylcholinesterase activity. This technique was used to evaluate the effect of ligation on segments in the ventral CNS. When embryos were ligated prior to cellularization (60 min) fewer segmental ganglia developed in posterior fragments than when embryos were ligated at the blatoderm stage (3 h). This result is consistent with previous ligation experiments in which hypodermal segments were counted (Schubiger and Wood 1977). The number of ganglia scored exceeded the number of hypodermal segments scored especially after ligations at 60 min. Possible explanations for this difference are discussed.