508 WALTER EDWARD COLLINGE. 
In P. folium there are present all the canals and sensory 
organs previously referred to, excepting the ampullary canals, 
which have not as yet been observed in any order of fishes but 
the Elasmobranchii. 
The system extends from the dorsally deflected terminal 
portion of the trunk, which I shall speak of as the dorsal 
caudal fin, to the tip of the rostrum. There is a certain 
polarity about the system, it having its greatest development 
on the head and rostrum, and the posterior end of the trunk 
of the body and the dorsal caudal fin. Short branches of the 
lateral canal cover each side of the body, terminating in series 
of cluster pores. 
The general distribution of the canals and branches is as 
follows : 
The lateral canal commences about 180 mm. from the tip of 
the dorsal caudal fin and passes along the side of the body, 
giving off in its course the above-mentioned branches, which 
are mostly ventral ones. The cluster pores on these branches 
exhibit slight modifications from those upon the head. The 
canal at the anterior end of the body makes an upward curve 
and enters upon the skull in the post-temporal region as a 
dermal canal. Traversing the region for a short distance, it 
enters a canal bone and gives off a small branch on the inner 
side of the canal in the occipital region. The canal is con- 
tinued forwards in a series of canal bones lying on the dorsal 
surface of the dermo-sphenotic of Bridge, giving off a short 
lateral branch at the most posterior end of the bone. In the 
anterior portion the canal bone spreads out in a wing-like 
manner and divides into two dorsal branches, viz. a supra- and 
sub-orbital, and a ventral branch, the hyomandibular (PI. 39, 
fig. 1). The first-mentioned branch passes upwards and for- 
wards, skirting the lateral border of the frontal; it then takes 
a downward course along the dermo-ect-ethmoid and _ passes 
between the nasal openings, below which it unites with the 
sub-orbital branch. The sub-orbital branch is given off in the 
anterior portion of the dermo-sphenotic, and runs as a bony 
canal posterior and inferior to the orbit, meeting anteriorly 
