674 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [120] 



EXPLANATION OF THE REFERENCE LETTERS USED IN THE PLATES. 



A indicates the position of the embryo's head. 



a. auricle. 

 ab. air bladder. 



al. allantois, median vesicle into which the segmental ducts open. 

 ar. dorsal aorta. 

 as. asterisk. 

 au. auditory canal. 



B. indicating ihe position of the tail of the embryo. 

 ba. bulbus arteriosus. 

 bf. pectoral or breast fins. 

 bl. blastopore. 



c. caudal vein. 



cc. pericardiac cavity. 

 ce. cerebellum. 



ch. notochord or chorda dorsalis. 

 chs. chorda sheath. 

 c. pi. cell plate. 

 cv. first cerebral vesicle or neural sinus. 



d. yelk or dentoplasm. 



e. mesenteron or primitive gut. 



ep. epiblast, cuticular layer mostly. 



ff. primitive lateral fin-folds. 



fb. cerebrum or fore-brain. 



fc. choroidal fissure. 

 h. heart. 



hy. hypoblast ; hypophysis in Fig. E. 

 inf. infundibulum. 



(/. gills, and inferior cranial arches. 

 gd. germinal disk. 

 i. intestine. 



ic. intestinal constriction, ijylorus. (T) 

 Ev. Kupfier's vesicle. 



I. lens. 

 liv. or h. liver. 



m. mouth. 



mo. medulla oblongata. 

 mc. medullary canal. 

 ms. medulla spinal ; spinal cord. 

 mes. caudal mesoblast. 



mi and mi^. micropyle. 

 mJc. Meckel's cartilage. 

 mp. muscle-plate. 



n. nucleus; neurula in Figs. E, F, H, I, J, K. 

 na. nasal pit. 



nc. neurenteric canal or strand of cells. 



vf. nerve filament. 

 <B. oesophagus. 



op. optic vesicles. 

 p. point where the dorsal aorta joins the caudal vein. 



j)p. polar protoplasmic prominence. 



