242 On the Evolution of the Vertebrata, [ March, 
found it convenient to lie on one side, a habit which would appear 
to result from a want of motive energy. The fins are very ineff- 
cient organs of movement in them, and they are certainly no 
rivals for swift-swimming fishes in the struggle for existence, ex- 
cepting as they conceal themselves. In order to see the better’ 
while unseen, the inferior eye has turned inwards, z. e., upwards, 
and finally has penetrated to the superior surface, so that both 
eyes are on one side. This peculiarity would be incredible if we 
did not know of its existence, and is an illustration of the extra- 
ordinary powers of accommodation possessed by nature. The 
Heterosomata can only be considered a degenerate group. 
The double bony floor of the skull of the Distegous percomorph 
fishes is a complication which places them at the summit of the 
line of true fishes. At the summit of this division must be placed 
the Pharyngognathi, which fill an important role in the economy 
of the tropical seas, and the fresh waters of the Southern hemi- 
sphere. By means of their powerful grinding pharyngeal appara- 
tus they can reduce vegetable and animal food inaccessible to 
other fishes. The result is seen in their multifarious species and 
innumerable individuals decked in gorgeous colors, and often 
reaching considerable size. This is the royal order of fishes, and 
there is no reason why they should not continue to increase in 
importance in the present fauna. 
Very different is the line of the Plectognathi. The probable 
ancestors of this division, the Epilasmia (Chztodontide, etc.), are 
also abundant in the tropical seas, and are among the most bril- 
liantly colored of fishes. One of their peculiarities is segn in a 
shortening of the brain-case and prolongation of the jaws down- 
wards and forwards. The utility of this arrangement is probably 
to enable them to procure their food from the holes and cavities 
_ of the coral reefs among which they dwell. In some of the gen- 
era the muzzle has become tubular (Chelmo), and is actually used 
as a blow-gun by which insects are secured by shooting them 
with drops of water. This shortening of the basicranial axis has 
produced a corresponding abbreviation of the hyoid apparatus. 
The superior pharyngeal bones are so crowded as to have become 
a series of vertical plates like the leaves of a book. These char- 
acters are further developed in the Plectognathi. The brain-case 
i is very small, the face is very elongate, and the mouth is much 
eae The bones surrounding it in each jaw are codssified. 
i 
