524 ALLIS. [Vou. II. 
formed between the organs along the bottom of the general 
depression. It is deepest near the newly formed section of 
canal; and into it the canal opens, the sides of the openings 
passing gradually into the walls of the channel. The limits of 
the canal are clearly defined by a sharp change in direction of 
the bottom of the channel, the canal leading inward at some- 
thing of an angle, the walls of the canals and pits always being 
much lighter in color than the outer surface. 
The openings of these short sections of canal may be called 
half-pores because, with a few exceptions, all the primary pores 
in the developed system are formed by the fusion of two of 
them. After its formation the short canal increases in length 
by the continued coalescing of the edges of the channel im- 
mediately beyond it, and the two half-pores are pushed apart 
along the line of the canal toward other pores which are in a 
similar way approaching them from adjoining sections. This 
process in Amia is continued until the pores meet and unite, 
thus forming a continuous canal with a primary pore and tube 
between every two consecutive organs; but it may be arrested, 
in which case an interrupted canal will be formed, as in the 
post-temporal part of the infra-orbital in Esox lucius and along 
the canal of the lateral line in Ophidium (No. 5, p. 39). At 
each end of a continuous canal formed in this manner it is evi- 
dent there must be a pore, which, if it cannot unite with a pore 
of some other line to form a double system, must always remain 
a half-pore or terminal opening. Such terminal openings are 
retained in Amia in pores 1 and 8 supra-orbital and 1 operculo- 
mandibular. The other terminal opening of the opercular line, 
pore 17, unites with pore 17 infra-orbital to form a double sys- 
tem. In the infra-orbital line pore 6 is a terminal one, and pore 
22-1 a double one, formed at the other end of the line where it 
joins the lateral canal of the body. In the anterior commissure 
one terminal opening has disappeared on the top of the snout 
where the two lines meet, and the other has fused with the sec- 
ond pore of the main canal to form what has been called pore 5 
infra-orbital. 
Cut Io is a diagrammatic representation of the formation and 
' subsequent subdivision of a primary pore. These two processes 
are continuous and essentially similar; for even in the adult, 
two pores if forced together from want of space fuse, as fre- 
