No. 3.] LATERAL LINE OF AMIA. 495 
primary pore with a single unbranching tube leading to it from 
one of the central canals. This condition is found in fishes 
about one month old, or from 40 to 60 millimetres long; but as 
the different systems pass through it at slightly different times, 
no single specimen or age fully represents it. 
There are normally at this stage ninety-three primary pores 
and tubes on the entire head, — forty-six on each side and a me- 
dian one in the supratemporal cross-commissure. This median 
pore is the last one developed, and its formation marks the end 
of a first period, in which the canals and the primary tubes 
and pores are developed, and the beginning of a second and last 
in which the tubes and pores begin the dividing, shifting, and 
multiplying which result in the complicated arrangements found 
in the adult. Fig. 49, Pl. XLII., is a diagrammatic representation 
of this stage, showing the course of the canals and the position 
of the primary pores and tubes. Fig. 13, Pl. XX XIV., shows the 
arrangement of the pores on the head of a fish 30% millimetres 
long, in which the lateral system is in a somewhat earlier stage 
of development; and Figs. 14, 15, and 16, Pl. XXXV., that on 
the head of a fish 78 millimetres long, in a more advanced con- 
dition. 
At the stage represented in the diagram, pores I and 2 supra- 
orbital, and 2, 3, 4, and § infra-orbital, are arranged nearly in a 
circle around the nasal tube, No. 5 infra-orbital lying somewhat 
out of the circle, directly in line with pores 1 and 2 supra-orbital 
in front, and 7 and 8 infra-orbital behind. A dermal depression 
separates pores I supra-orbital and 5 infra-orbital as in the adult. 
Pore 8 infra-orbital lies in a well-marked corner formed by the 
anterior end of the supramaxillary furrow, which turns sharply 
upward in a curved line. Pores 9 to 12 lie below the eye, form- 
ing with No. 8 a straight line extending directly backward. Pores 
13 and 14 lie behind the eye, and above and behind it is the 
double pore, 15 infra-orbital and 7 supra-orbital, which, in the 
674-millimetre specimen has undergone its first division. Pore 16 
is in process of division in this specimen, lying about mid-way 
between the double pores, 15-7 and 17-17, formed at the point 
where the infra-orbital and operculo-mandibular canals unite. 
Then follow pores 18 and Ig as a pair a little in front of the 
upper end of the opercular opening, and pores 20, 21, and 22-1 
above this opening. 
