180 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 
series of organs in the adult. At points on these lines the sensory 
areas are developed by the differentiation of two kind of cells, the 
supporting cells which extend through the epidermis from the corium 
to the free surface, and the sensory cells which reach from the surface 
only part way to the base. The latter are pear-shaped and bear 
cuticular hairs or bristles on their free ends (fig. 179), while the deeper 
ends are embraced by the non-medullated fibrils of the lateralis system 
of nerves, which follow the lines of organs, and in development keep 
pace with their extension. These sensory areas are the nerve hillocks 
or neuromasts already referred to. 
Fic. 179. Fic. 180. 
Fic. 179.—Sense organ of lateral line of Diemyctylus (aquatic form) freely after Kings- 
bury, C, cone cells; s, spindle cells. 
Fic. 180.—Developing lateral line organ on one side of head of A mia, showing method 
of closure of grooves to canals, after Allis. a7, anterior naris; io, so, infra- and supraorbital 
lines; px, posterior naris. 
In the cyclostomes and aquatic amphibia each sensory patch 
sinks into a separate pit (fig. 179), but in all other itchhyopsida the 
lines of organs sink in the same way, the patches being connected by 
grooves. In Chimera these grooves remain open, but in all others they 
are closed except at certain points where pores connect the canals 
formed by the closed grooves with the exterior. In this way the sensory 
areas come to lie in canals beneath the surface, water obtaining access 
to them through the pores. In many teleosts (fig. 181) the pores 
pass through notches or openings in the scales, while on the head the 
canals themselves frequently run through some of the cranial bones. 
Of considerable morphological importance, especially in connection with the 
morphology of the ear, are the facts that the sensory areas multiply by elongation, 
followed by division, and that the pores themselves increase in the same way 
