Expression of NvRx. In situ hybridization using a 1419 bp probe of rx. The asterisks denote the blastopore or oral end. (a,b) No expression is detected in the egg or early cleavage stages. (c,d) Mid gastrula stages showing expression around the aboral ectoderm. (e) Late gastrula stage showing a band of expression towards the aboral pole. (f) The same embryo in (e) as viewed from the aboral pole, showing a lack of expression where the future apical tuft (at) will form. (g-j) Planula stages, with (i) showing a surface view of the patchy expression. (k) Polyp stage, showing a close-up view of expression in the ectoderm of the tentacles (t).