OF THE MARSIPOBRANCH FISHES. 
457 
Plate. 
26 
33 
33 
3 3 
33 
5? 
33 
3 3 
33 
33 
33 
33 
33 
Fig. 
Humber of 
times 
magnified. 
Petromyzon jluviatilis (larva, 6 inches long) 
1 
Third of a series of thin vertically-transverse sections 
through head and branchial region. 
12 
2 
The same ; fourth section. 
12 
3 
The same ; fifth section. 
12 
4 
The same ; sixth section. 
12 
5 
The same ; seventh section. 
12 
6 
The same ; eighth section. 
12 
7 
The same ; ninth section. 
12 
8 
The same ; tenth section. 
12 
9 
The same ; eleventh section. 
12 
10 
The same ; tivelfth section. 
12 
11 
The same ; fifteenth section. 
12 
12 
The same ; sixteenth section. 
12 
13 
The same ; seventeenth section. 
12 
