No. 3.] LATERAL LINE OF AMIA. 529 
Figures 6 to 12 show the formation of these canals in three 
specimens, —one 114 millimetres long (Figs. 6 and 7), one 14 
millimetres long (Figs. 8 to 11), and one 18 millimetres (Fig. 
12). As shown in these figures, the supra-orbital canal in front 
of organ 7 is inclosed in two sections containing three organs 
each, and the mandibular canal in a single section containing 
the first nine organs of the line. In the infra-orbital line organs 
3 to 7 are inclosed together in a Y-shaped section of canal, and 
then organs I and 2, and 8, 9, 10. The median pore No. 1 
formed in this process is shown in Fig. 11. It afterwards 
entirely disappears. 
Organ 5 infra-orbital is normally the first one in the whole 
lateral system to be inclosed, and the formation of that part of 
the canal in which it lies is closely associated with the develop- 
ment of the nose. In Fig. 1 the nose is shown as a simple pit 
lying beyond the line of the infra-orbital canal. It is at first 
round and deep, but it soon becomes oblong, as shown in Fig. 
4, and is then inclosed exactly as the canals of the lateral sys- 
tem are, a short section of canal being formed open at both ends 
and continuous behind with the Y-shaped open depression of 
the infra-orbital line. This stage is shown in Fig. 6, an unpig- 
mented surface line still showing where the canal has closed 
over the nasal pit. The whitish cord of the infra-orbital line 
extends beyond organ 5 toward and partly into the posterior 
one of the two openings. In the 14-millimetre specimen, Fig. 
8, organ 5 has been inclosed, and the half-opening, destined to 
become pore 6, stands facing the posterior naris, connected with 
it by a deep depression. At this stage these two openings 
appear like two half-pores about to fuse, but this resemblance 
soon disappears. In the 18-millimetre specimen, Fig. 12, the 
two pores still open into a large common depression, but it is 
becoming shallower; in Fig. 13, a 31-millimetre specimen, it has 
nearly disappeared ; and in Fig. 14, entirely so, pore 6 now hav- 
ing a position in front of the naris instead of below it as at 
first. The formation of pore 5 infra-orbital from three half- 
pores is shown in Fig. 8. 
In the opercular line the central part of the canal is formed 
at an early age. Organs 13 and 14 are the first to be inclosed 
(Fig. 12), then organs 12 and 15, and finally, at a much later 
period, organs 11 and 16. During this stage of its development 
