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INFLUENCE OF LATERAL-LINE CANALS 327 
The relation of the canals to the early deposition of osseous 
material is shown in figures 3 and 4. Here the bony substance 
is deposited in spicules and in granules immediately adjacent 
to the circumference of the lateral-line canals. Deposition of 
bone is not brought about by nervous stimulus arising from the 
lateral-line end organs. ‘The sense organs of the supra-orbital 
canals (fig. 3), if they exist at all at this point, are enclosed in 
bone, and are thus not in relation with the osteogenic areas. 
The fact that the ossification around the supra-orbital canals is 
segmental in the larva suggests the presence of tubules and der- 
mal pores in the young which are lost in the adult. 
Regarding the later development of the osseous tubes around 
the lateral-line canals, MeMurrich (’84, p. 279) states ‘‘the os- 
seous tube does not remain distinct but fuses with the subja- 
cent bone, whether formed in membrane or perichondrally.” 
CONDITION OF THE SKULL BONES IN AMIURUS AT 50 MM. 
Nearly all the cranial elements are fully established at this 
stage, excepting the nasal, the lacrimal, and the suborbitals, 
which are lateral-line canal bones. The ossification of the skull 
in Amiurus is the reverse of the usual antero-posterior embryonic 
development, since the posterior cranial elements are the first 
to be fully established. 
The lacrimal is represented as a triradiate mass of aggregated 
spicules arranged around the anterior termination of the sub- 
orbital canal. The nature of the ossification is intermediate 
in character between that of the supraorbital canal, where it is 
in threads, and the suborbital chain, where it is in granules. 
The nasal, formed around the anterior end of the supraorbital 
canal, is composed of spicules arranged around the canal. The 
suborbital chain of bones is still undifferentiated and the condi- 
tion of the osseous material is shown in figure 4. The supra- 
ethmoid is fully formed, and has been developed apparently 
entirely independent of any influence from the lateral-line system. 
The course of the canals through the sphenotics and frontals 
is clearly evident, due to a dense deposition of calcium in granu- 
lar form on the walls of the canals. The osseous tube has not 
yet fused with the subjacent bone. 
