Fig. 1. Section from the caudal region of a Pristiurus embryo belonging to stage H. Zeiss C, ocul. 1. Osmic acid specimen.
It shews (1) the constriction of the subnotochordal rod (x) from the summit of the alimentary canal. (2) The formation of the body-cavity in the muscle-plate and the ventral thickening of the parietal plate.
Fig. 1a. Portion of alimentary wall of the same embryo, shewing the formation of the subnotochord rod (x).
Fig. 2. Section through the caudal vesicle of a Pristiurus embryo belonging to stage H. Zeiss C, ocul. 1.
It shews the bilobed condition of the alimentary vesicle and the fusion of the mesoblast and hypoblast at the caudal vesicle.
Fig. 3a. Sections from the caudal region of a Pristiurus embryo belonging to stage H. Zeiss C, ocul. 1. Picric acid specimen.
It shews the communication which exists posteriorly between the neural and alimentary canals, and also by comparison with 3b it exhibits the dilatation undergone by the alimentary canal in the caudal vesicle.
Fig. 3b. Section from the caudal region of an embryo slightly younger than 3a. Zeiss C, ocul. 1. Osmic acid specimen.
Fig. 4. Section from the cardiac region of a Pristiurus embryo belonging to stage H. Zeiss C, ocul. 1. Osmic acid specimen.