62r 



is extriiordiiKirily tliick over the jj^i'oater iwrt of the 

 l)0(h'. Ill ;i Suntisli 9(!5 luiu. loiiii' the skin on tlic 

 trunk, according to {'lelaxp, was ahout 25 nun. thick". 

 'I'lie rigidity of tlie skin is increased by the spiny and 

 nodose, small, osseous tubercles'' which are densely spread 

 over its surface, and wiiich give tlic skin both on the 

 I)odv and tlie tins a shagn^ened appearance. lUit a 

 rather broad band of thinner and looser skin, with more 

 granulated or even smooth surface, runs on each side, 

 along tlie vcrv margin of the body, from the vent along 

 tlie 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 fins, admits of 

 tlie bending of these two fins at right angles to the 

 sides of tlie body. Tlie first six rajs in these fins are 

 thick and stiff, neither articulated nor branched, and 

 suddenly increase in length, thus forming the greater 

 part of the anterior margin of the fin — only the apex 

 belongs to tlie seventh ray, which is branclied. Tiie 

 jiosterior rays, again, suddenly decrease in length be- 

 liind, are branched, and expand backwards at the tip 

 like a fan. Thus, the whole of this apparatus forms, to- 

 gether with the caudal fin, a swimming-blade, elastic 

 behind, wiiich by alternate movements to right and 

 left of the dorsal and anal fins drives the fish forward, 

 just as a boat is propelled by sculling. The compara- 

 tivelv shoi't pet'toral fins, which, as well as the other 

 fins, are rough witli 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 ]>oint 

 between the tip (jf the snout and tlie Iieginning of the 

 dorsal or the anal fin. Tiiej- are inserted horizontally, 

 as in the Opah, and move up and down, their true 



function thus being proliably to maintain the equi- 

 librium of tile bod\-. dust in front of the insertion of 

 tlie jicctoral fin, with iieight about equal to the Icngtii 

 of this insertion, lies the traiisvei-sely set gill-ojiening 

 on eacli side of the body, elliptical in shape, but pointed 

 at both ends, and with tlie anterior liaif covered with 

 a thin skin', wdiicli is a continuation of the true branch- 

 iostegal membrane, while the anterior margin is formed 

 by the skin itself, which eovei'S the 0})erculum. These 

 small openings are the only external boundaries between 

 the head and tlie 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 

 (',2 — 1 metre long) between Vs ''»d ^/m 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'. In old specimens, which have their short 

 snout tipiied with the hard osseous disk, this disk forms 

 the extreme end of the snout. In }'oung specimens 

 the mouth is set exactly at the tip of the snout, and 

 shows between the thin lips, whicli 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 otlier, which are gradually worn awa}' 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 ram. 

 in breadth, or rather less than the longitudinal diameter 

 of the eye. The ejes 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 ventral'; their 



" 111 a large Snntish 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, whicli was unusually large, GooDSlR found the thickness of the skin 

 at certain spots to be 152 mm. 



' 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 tlicy bear radiating stri.-p, and arc irregularly incised and dentatcd at the margin, the 

 teeth of one tubercle fitting into the incisions in the next. 



' 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-openings on each side that was given 

 by Rafinesque to his genus Diplanchias. 



■' "Der schwimmende Kopf": Blocii, 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. 



' 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. 



•'■ 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 Trachi/pterus, p. 319. 



