286 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
EXPLANATION OF PLATE XXXIX. 
Fig. 9. Embryo of sterlet, still more advanced, after the closure of the medullary groove and forma- 
tion of spinal cord; twenty-four embryonic segments visible and the two prouephric or 
Wolffian cauals formed on either side, while in front (upper pole of figure) the cephalic plates 
of mesoblast appear on either side of the rudiments of the brain. After Salensky. 
Fig. 10. Embryo of the sterlet, showing its anterior end from above ; three visceral arches, frontal 
process, the cerebral vesicles, auditory pits, Wolffian ducts, and twelve embryonic segments 
are developed. After Salensky. 
Pig. 11. More advanced embryo of the sterlet, showing the anterior jjart of the body and head. Audi- 
tory and nasal organs, heart, vitelline circulation, and brain more developed than in preced- 
ing figure. After Salensky. This figure represents a stage slightly more advanced than my 
figure 3 of the embryo of the common sturgeon. 
