JOURNAL OF MICROSCOPICAL SCIENCE. 



EXPLANATION OF PLATES XIII, XIV & XV, 



Illustrating Mr. F. M. Balfour's Paper on the development 

 of the Elasmobranch Fishes (Dog-fishes). 



Complete List of Reference Letters. 



n. Peculiar nuclei formed in the yolk. 

 «'. Similar nuclei in the cells of the blastoderm. 

 J b d. Formative cell probably derived from the yolk. 



ny. Network of lines present in the food-yolk. 

 1/ k. Yolk spherules. 



I y. Line of separation between the blastoderm and the yolk. 

 e p. Epiblast. 

 e fl. Epidermis. 

 1 1. Lower layer cells. 

 m. Mesoblast. 

 hy. Hypoblast. 

 s c. Segmentation cavity. 

 e s. Embryonic swelling. 

 e r. Embryonic rim. 



e b. Line indicating the edge of the blastoderm. 

 m g. Medullary groove. 

 m c. Medullary canal. 

 t s. Caudal lobes. 

 n a. Cells which help to close in the alimentary canal, and which 



are derived from the yolk. 

 V p. Vertebral plates. 



h. Head. 

 a I. Alimentary canal. 

 c h. Notochord. 



c K. Thickening of hypoblast to form the notochord. 

 p p. Pleuro-peritoneal cavity. 



p p'. Remains of pleuro-peritoneal cavity in the head. 

 pr V. Protovertebrse. 



so s. Stalk connecting embryo with yolk-sac. 

 V c, 1, 2, 3, &c. 1st, 2nd, and 3rd &c. visceral clefts. 

 op. Eye. 



I. Olfactory pit. 

 au V. Auditory vesicle. 

 V. Eifth nerve. 

 VII. Seventh nerve. 

 g I. Glosso-pharyngeal nerve. 



V. Vagus nerve. 

 tp n. Spinal nerve. 

 8 0. Somatopleure. 

 s p. Splanchnopleure. 

 X. Peculiar body underlying the notochord derived from the 

 hypoblast. 

 a 0. Dorsal aorta, 



