Fig. 2. CNS cell count comparison of mid-stage 16 and stage 17 wt and H99 embryos. White and black bars represent cell counts from wt and H99 embryos, respectively. For exact numbers see text. Asterisks mark statistically significant differences between wt and H99 (P<0.001, two-tailed t-test). The thoracic CNS shows a difference between wt and H99 only at stage 17. The abdominal part of the CNS of H99 embryos contains more cells already at mid-stage 16, and the difference increases further at stage 17. th, thorax; abd, abdomen.