No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 713 
and they form, with the notochord, the principal part of each 
vertebral body. Membrane bone has, however, even in 20 mm. 
larvae, begun to form between the processes, and between 
those of opposite sides. There is not the slightest indication 
of a separation of the vertebra into two lateral halves, or into a 
dorsal and a ventral half. 
The dorsal process, on each side, is much larger than the 
other processes, and is wholly independent of them. Of the 
other two the lateral one is the larger, but it is not independ- 
ent of the ventral one, the two being connected by a thin strip 
of cartilage, which extends downward from the anterior end of 
the lateral process to the posterior end of the ventral one. The 
ventral processes lie on either side of the dorsal aorta, and, in 
old larvae, are sometimes continuous at their hind ends, dorsal 
to the aorta. 
The dorsal arches lie, as in the adult, with their bases 
wedged in between two succeeding dorsal processes, but they 
are not continuous with either process. The fusion of the 
arches, at their bases, with the dorsal process next in front 
of them, is thus a secondary arrangement, arising in post-larval 
stages. That this late and secondary fusion of the arch proper 
with the vertebral body is not peculiar to Amia, and that it is 
probably the regular method of development in all bony ganoids 
and teleosts, if not in all animals, is shown by Sagemehl’s 
statement (No. 107, p. 587) that even in the adult of the 
Cyprinidae and Characinidae, the dorsal arches are not ‘fest 
verbunden”’ with the vertebral bodies. The cartilaginous pad 
found in the adult Amia, between each arch and the next 
posterior dorsal process, is not found even in 50 mm. speci- 
mens. It, also, must therefore develop in later stages. 
The vertebral processes all rest, at their bases, upon a thin 
layer of strongly refractive material, apparently bone, formed 
around the notochord. This layer is considered by Schmidt, 
in the adult Amia, as the “selbstandig verknécherte dussere 
zellige Chordascheide”’ (No. 110, p. 754), and by Hasse (No. 
52, Fig. 14), as the “‘ Faserscheide der Chorda,” a part of the 
cuticula chordae. What is apparently the same layer in teleosts 
and selachians is called by Géppert (No. 48) the ‘“Chorda- 
