No. 3-] THE PRONEPHRIC DUCT IN SELACHIANS. 125 



derm for such a distance that the sudden turn and fusion with 

 the ectoderm was very marked. 



Fig. 3 (a, b, c, d, e) shows five successive sections at the end 

 of the left pronephric duct of an embryo 5 mm. long (about 33 



FIG. 3. 



somites). Fig. 4 (a, b) shows two sections near the end of the 

 right duct of the same embryo. Fig. 5 (a, b, c, d, e,f) shows 

 the conditions at the end of the left duct of another embryo 

 5 mm. long (about 30 somites). Between c and/ ten sections 



Fir,. 4. 



similar in character to e are omitted. In /the two cells which 

 form the end of the duct are deeply stained and readily distin- 

 guished from the others. In this case the fusion is of unusu- 

 ally long duration. In addition to many series like the above, 



