Fig. 5. Amphi-hairyA, Amphi-hairyB, Amphi-hairyC and Amphi-hairyD genes expression in amphioxus larvae by whole-mount in situ hybridisation. Lateral views (A,D,F,J) have anterior towards the left and dorsal upwards. In dorsal and ventral views (I,K,N), anterior is towards the right. In transverse sections (B,C,E,G,H,L,M), dorsal is upwards looking from a posterior position. (A) Amphi-hairyA expression in the endoderm and the posterior dorsal nerve cord of an amphioxus larva. Scattered positive cells are in the middle gut are indicated by a double arrow and expression in the left anterior gut diverticulum is indicated by an arrow. (B) Cross-section through level i in A showing the expression of Amphi-hairyA in the preoral pit (arrow). (C) Cross-section through level ii in A showing the expression of Amphi-hairyA in the gut (arrow) and the posterior neural tube (asterisk). (D) Amphi-hairyB expression in the anterior half of the dorsal nerve cord. The gap in the anterior neural tube domain is shown by a double arrow. (E) Cross-section through level i in D showing the expression of Amphi-hairyB in the neural tube (asterisk). (F) Lateral view of an amphioxus larva showing Amphi-hairyC expression in the posterior tail bud, and in the anterior endoderm (arrow indicates the pharyngeal endoderm, and asterisk indicates the preoral pit). (G) Cross-section through level i in F showing the expression of Amphi-hairyC in pharyngeal endoderm (arrow). (H) Cross-section through level ii in F showing the expression of Amphi-hairyC in the posterior mesoderm. (I) Dorsal view of the specimen in F showing the Amphi-hairyC expression within the tail bud. (J) Lateral view of a larva showing Amphi-hairyD expression in the anterior club-shaped gland (asterisk) and the presumptive first and second gill slits (arrows), and in the posterior mesoderm. (K) Ventral view of the specimen in J. (L) Cross-section through level i in J showing the expression of Amphi-hairyD in the club-shaped gland (arrow). (M) Cross-section through level ii in J showing the expression of Amphi-hairyD in the posterior mesoderm. (N) Dorsal view of the specimen in J showing the Amphi-hairyD expression within the tail bud.