SUN FISH. 
627 
is extraordinarily thick over the greater part of the 
body. In a Sunfish 965 mm. long the skin on the 
trunk, according to Cleland, was about 25 mm. thick". 
The rigidity of the skin is increased by the spiny and 
nodose, small, osseous tubercles 4 * which are densely spread 
over its surface, and which give the skin both on the 
body and the tins a shagreened appearance. But a 
rather broad band of thinner and looser skin, with more 
granulated or even smooth surface, runs on each side, 
along the very margin of the body, from the vent along 
the bases of the anal, caudal, and dorsal tins. This 
band of flexible and movable skin, which is folded 
round the bases of the dorsal and anal tins, admits of 
the bending of these two fins at right angles to the 
sides of the body. The first, six rays in these tins are 
thick and stiff, neither articulated nor branched, and 
suddenly increase in length, thus forming the greater 
part of the anterior margin of the tin — only the apex 
belongs to the seventh ray, which is branched. The 
posterior rays, again, suddenly decrease in length be- 
hind, are branched, and expand backwards at the tip 
like a fan. Thus, the whole of this apparatus forms, to- 
gether with the caudal tin, a swimming-blade, elastic 
behind, which by alternate movements to right and 
left of the dorsal and anal tins drives the fish forward, 
just as a boat is propelled by sculling. The compara- 
tively short pectoral tins, which, as well as the other 
tins, are rough with small osseous tubercles on both 
sides, are of rounded form, with the first, and last, rays 
simple, the others multifid at the tip, and the middle 
ones (the fifth and sixth) longest. They are set, half- 
way up the body and just behind the middle point 
between the tip of the snout and the beginning of the 
dorsal or the anal fin. They are inserted horizontally, 
as in the Opah, and move up and down, their true 
function thus being probably to maintain the ecjui- 
librium of the body. Just in front, of the insertion of 
the pectoral tin, with height, about, equal to the length 
of this insertion, lies the transversely set, gill-opening 
on each side of the body, elliptical in shape, but pointed 
at both ends, and with the anterior half covered with 
a thin skin c , which is a continuation of the true branch- 
iostegal membrane, while the anterior margin is formed 
by the skin itself, which covers the operculum. These 
small openings are the only external boundaries between 
the head and the body. This circumstance has caused 
the comparison of the whole fish to a swimming head**. 
The head of the Sunfish (from the tip of the snout 
to the gill-openings) measures in young specimens 
(7 a — 1 metre long) between 7s and 3 / 10 of the length 
of the body. In older specimens, which acquire a more 
elongated form of body, it becomes comparatively some- 
what, smaller, sinking to at least, 29 % of the length of 
the body 6 . In old specimens, which have their short 
snout tipped with the hard osseous disk, this disk forms 
the extreme end of the snout. In young specimens 
the mouth is set, exactly at the tip of the snout, and 
shows between the thin lips, which only partially hide 
them, its two white dental disks, that of the upper jaw 
hooked at the tip, that of the lower jaw even. Behind 
(within) these disks we find in young specimens 4 or 5 
similar disks or rows of divided, transverse disks, close 
behind each other, which are gradually worn away in 
course of time, until they disappear. The gape is small, as 
in all the Plectognates; in a Sunfish 47 cm. long it can be 
opened to a height of only 33 mm. and measures 24 mm. 
in breadth, or rather less than the longitudinal diameter 
of the eye. The eyes are set very low, in comparison with 
their position in the rest of the Plectognates, but much 
nearer to the dorsal margin than to the ventraP; their 
4 In a large Sunfish dissected by Turner and Goodsir (Nat. Hist. Review 1862, p. 185) the skin varied in thickness on different 
parts of the body between 6 and 100— 127 mm. In another specimen, which was unusually large, Goodsir found the thickness of the skin 
at certain spots to be 152 mm. 
6 The osseous tubercles vary in size, large and small being interspersed with each other; but even the largest ones in large Sunfish 
are scarcely of the size of small pins’ heads. At the base they bear radiating striae, and are irregularly incised and dentated at the margin, the 
teeth of one tubercle fitting into the incisions in the nest. 
e When this membrane lies in folds, or when it bursts — as often happens in stuffed specimens — it may appear as though there 
were two gill-openings on each side; and this is perhaps the explanation of the character of two gill-openiDgs on each side that was given 
by Rafinesque to his genus Diplanchias. 
d “Der schwimmende Kopf”: Bloch, 1. c. From the form of the snout and the small size of the mouth the fish also acquires a 
singular resemblance, which has struck many, to the human head. 
e According to Campbell’s measurements of a specimen 236 cm. long (Proc. Nat. Hist. Soc. Glasg., vol. V, 1881 — 82, p. 178) this 
percentage may sink to 24'7. 
f In the specimen which Hasting examined, he found (1. c.) an asymmetry in the position of the eye (the right eye — like the right 
pectoral fin — situated perceptibly higher than the left), which he proposed to explain by the habit possessed by these fishes, of lying at the 
surface and swimming on one side. Cf. above, on Trachypterus , p. 319. 
