No. 3.] LATERAL LINE OF AMIA. 499 
If the bones containing the two anastomosing canals have anchy- 
losed, or the two canals lie in the same bone, then both the pore 
and the trunk belonging to it entirely disappear. 
The ethmoid in Amia is formed by the union of the two bones 
usually found in other fishes. At the line of union of these 
two bones, where the main infra-orbital canals of opposite sides 
unite, a single median pore and trunk have been formed and 
disappeared, as younger stages show. In like manner a pore 
and trunk have disappeared on either side at the point where 
the supratemporal commissure joins the main infra-orbital, these 
two canals here lying in the same bone, the extrascapula. 
These two are the only trunks and pores that have disappeared 
in the entire system in Amia. In the adult, with two exceptions 
only, all of the primary tubes, which at younger ages issue from the 
main canals between consecutive bones, become partly or entirely 
wnclosed tn one or the other of these bones. The two exceptions 
are trunk 4, supra-orbital, and the double trunk 17—17, which, 
even in the adult, lie wholly in the dermis. 
2. Number and Position of the Canal Organs. 
Between every two consecutive trunks, along the entire length 
of each canal, counting the double trunks twice, once along each 
of the anastomosing lines, and also counting the trunks that 
have disappeared, there is a single sensory spot or patch con- 
taining either a single well-developed organ of the kind called 
by Merkel (No. 12, p. 5) nerve-hillocks, and by Wright (No. 20, 
p. 480, note) neuromasts, or such an organ with one or more 
smaller ones developing at either end of it (Fig. 48, Pl. XLI.). 
These sensory patches always lie inside the dermal bones, 
and there are along the infra-orbital line two in the ethmoid, 
four in the antorbital, two in the lachrymal, one in each sub- 
orbital, two in the lower postorbital, one in the upper postorbi- 
tal, one in the postfrontal, three in the squamosal, one in the 
extrascapula, one in the suprascapula, and two in the supra- 
clavicula. Along the supra-orbital line there are three in the 
nasal, and four in the frontal; along the operculo-mandibular, 
seven in the dentary, three in the angular, and six in the pre- 
operculum ; and in each half of the supratemporal cross-com- 
missure three, all in the extrascapula, making forty in all on 
each side of the head. 
