142 
SCANDINAVIAN FISHES. 
way in number and length, though they never attain 
so great a length as the rays of the ventral tins. 
For a time all the last four rays in this tin are united 
by a membrane at the base (fig. 38, b), until at 
last the first ray appears just in front of the second 
and above the middle of the eye, being thus some 
distance from its future place on the snout, although 
the whole anterior part of the fin has advanced con- 
first rudiment of which appears on the ventral side of 
the notochord (fig. 38, a, +) in the form of two carti- 
laginous disks lying below the notochord in the mesial 
line of the body, the one in front of the other, just in 
front of the boundary of the pigment collected on the 
rudimentary, rod-like rays in the fin-membrane round 
the end of the tail. During the subsequent develop- 
ment of the fin these cartilaginous disks force the end 
Fig. 39. Young Lopliius piscatorius from the Mediterranean off Messina. 
After liuppELL and Gunther. 
Fig. 40. Young Lopliius piscatorius (— Lopli. eurypterus ) from Christiansund (Norway). Natural size. After v. Duben and Koren. 
a: seen from above; b: seen from the left. 
siderably from its original situation. The flat dermal 
flaps, the rudiments of the pectoral fins, have steadily 
grown, and been furnished with a greater number of 
rays; but even in the last stage examined by Agassiz 
(fig. 38, c) the tips of these rays are not yet free. Last 
of all appear the second dorsal and the anal fins, which 
occupy their ultimate situation and mutual position 
pretty closely from the first, and the caudal fin, the 
of the notochord upwards; and at their lower margin, 
which eventually becomes the hind margin of the tail 
(the hypural bones), the future rays of the caudal fin 
begin to appear (fig. 38, b). This is the usual course 
of development of the caudal fin in the osseous fishes, the 
caudal fin of which is thus originally ventral, like the 
greater (lower) part of the caudal fin in the heterocercal 
fishes, and is, strictly speaking, to be assigned to the same 
