52 LATERAL LINE 
ings already noted in Fig. 65. A process of this kind 
is carried to great lengths among the fishes which 
develop horn-like scales, as Amia, herring, or cod: in the 
scales of the lateral line region the distal tubules appear 
at the surface as a cluster of pores, as shown in Fig. 67, 
or in the detached scale of Fig. 66. 
The organs of the lateral line (of a bony fish) shown 
in section in Fig. 63 are regarded by the writer as of 
a highly modified character. They appear to have been 
derived from the conditions of Fig. 62; the end organ, 
S, corresponds with that, S, of the preceding figure; its 
size, however, has greatly increased, and the, intervening 
sensory tube has been lost; its metameral opening at 
the surface corresponds with that of Fig. 62; the nerve 
supply, 1, is now seen to have secured a more perfect 
relation to the end organs. 
The original significance of the lateral line system as 
yet remains undetermined. As far as can be judged from 
its development, it appears intimately, if not genetically 
related to the sense organs of the head and gill region of | 
the ancestral fish: in response to special aquatic needs, it 
may thence have extended further and further backward 
along the median line of the trunk, and in its later differ- 
entiation acquired its metameral characters. 
A significant feature of its development is its peculiar 
innervation. Its lateral tract is innervated by a specially 
evolved root of the vago-glossopharyngeal group, but its 
head region is supplied by a similar root of the facial 
nerve (perhaps also by the trigeminus; cf. Collinge, Ref 
p. 248). 
In view of this innervation, the precise function of this en- 
tire system of end organs becomes especially difficult to de- 
termine. Feeling, in its broadest sense, has safely been 
