No. 377-| AMIOID AND LEPISOSTEOID FISHES. 345 
out, but enough seems to be known to enable us to reach fairly 
good conclusions. It appears that in an early stage the noto- 
chord with its sheath becomes surrounded by a tube of cartilage. 
The bases of the upper and the lower arches are continuous 
with this tube (Fig. 5, %.a.). re between the bases of the 
successive arches the tube be- 
comes thickened into a ring 
(Fig. 5, tc); while on each 
side, just between the base of 
each upper arch and that of 
the corresponding lower arch, 
there is a gap in the cartilagi- 
nous tube. Now, it appears to 
me quite certain that the thick- 
ened ring of cartilage is com- 
posed of the four coalesced 
intercalated cartilages; and Dr." S erpe section trough nor 
Gadow and Miss Abbott enter- igel is dotted ; the bone shown by heavy black 
tain the mameview The tube (os ee A 
ë the ring of coalesced intercalated See 
is produced by the coalescence T Greats T A ame 
of these with one another and 
with the bases of the arches. When ossification sets in, the 
bony centers spread over the cartilage, probably from the bases 
of the arches, and, forming a ring, bind the arcualia of each 
segment together. No separate ossifications develop in the 
rings of intercalated cartilages, but these become divided each 
into an anterior and a posterior half, the anterior half forming 
the posterior end of the vertebra in front, the posterior half the 
anterior end of the vertebra behind. In Lepisosteus, therefore, 
the vertebral elements derived from the bases of the arches gain 
complete ascendency over the intercalated elements; in Amia, 
at least, the upper intercalated elements remain distinct and 
take a prominent part in the formation of the centrum. 
There is nothing to indicate that the vertebral rings of any 
of the genera assigned by Mr. Woodward to the Aetheospondyli 
have had a mode of development essentially different from that 
S, 
wae 
ae 
— 
sat 
1 Balfour and Parker, meget gorse of Lepidosteus, Mem. Ed., vol. i, p. 785, pls. 
xli, xlii. 2 Phil. Trans. Roy. Soc., vol. clxxxvi, p. 214, 1895. 
