174 BULLETIN OF THE BUREAU OF FISHERIES. 



The detached specimens in the National Museum collection were examined for 

 the kind and amount of torsion, but of course nothing could be told as to which side of 

 the fish they came from. 



Four specimens of L. tortua, all from the same fish, showed torsions of 45° inverse, 

 90° inverse, 720° direct (two complete revolutions), and 90° inverse, respectively. 

 Five specimens of L. variabilis from different fish showed respective torsions of 45° 

 inverse, 90° inverse, 0°, 100° inverse, and 45° inverse. In 20 specimens of L. cruciata 

 from different fishes, all the same size and carrying egg strings, there were 8 that showed 

 no torsion at all, 4 that showed 180° direct torsion, 2 that showed 180° inverse torsion, 

 while the torsions of the other 6 were, respectively, 150° inverse, 45° direct, 25° direct, 

 25° inverse, 100° direct, and 20° direct. 



A single specimen of tortua from Micropterus salmoides at Black Creek, N. C, had 

 its body twisted inversely in three complete revolutions (1080°) just behind the cephalo- 

 thorax. (See fig. 4, pi. vi.) In view of such extreme differences, the only rational 

 conclusion is that neither the amount nor the kind of torsion possesses any systematic 

 value whatever. 



The cephalothorax. — At the anterior end of the cephalothorax, between the bases 

 of the anterior horns, is a small button-shaped projection, its posterior margin fused 

 with the dorsal surface of the cephalothorax, its anterior margin projecting freely, its 

 dorsal surface more or less strongly convex. This may be called the head or cephalon 

 and it carries on its anterior free margin the two pairs of antennae, which are very similar 

 in all the species of the genus. (See fig. 5, pi. vi.) The first antennae are three or four 

 jointed, not including the basal protuberance to which they are attached, which is entirely 

 lacking in some species and which is immovable when present. Every joint is heavily 

 armed with long plumose setae along its anterior margin. Claus and some of the older 

 investigators ascribed five joints to these antennae, but their illustrations show that they 

 counted the basal projection as a fifth joint. (See fig. 42, pi. xi.) 



The second antennae are two jointed, again omitting the basal projection; the 

 proximal joint is unarmed, while the terminal joint ends in a tuft of setae and a single 

 large curved claw, making these appendages uncinate and attesting their prehensile 

 function. The same remarks apply to these appendages as to the first pair, Claus and 

 others designating them as three jointed. (See fig. 43, pi. xi.) The anterior margin of 

 the head projects between these antennae as a more or less pointed rostrum. 



In the center of the dorsal surface of the projecting head lies a proportionally large 

 eye, made up as in other parasitic copepods of three parts. The paired lateral portions 

 each surround a large spherical lens, while the unpaired anteroventral portion contains 

 a retinal layer of dark pigment. (See fig. 2, pi. vi.) In L. bar nimii Hartmann described 

 the eye as located on a special flattened plate on the dorsal surface of the head; the three 

 refractive bodies were spherical and of about the same size, and the unpaired one was 

 posterior. In L. esocina according to Claus and in all the American species examined 

 the paired lateral portions are much larger than the unpaired central one, and the latter 

 is anterior and ventral. Often nothing can be seen of this optical apparatus in external 

 view since it is buried some little distance beneath the skin and lies just above and 

 posterior to the supra-cesophageal ganglion. But in preserved and cleared material 

 as well as in serial sections it is always distinctly visible. (See fig. 65, pi. xiii.) 



Below the rostrum and between the antennae on the ventral surface of the head 

 is a short proboscis. Here again there has been diversity of opinion among the dif- 

 ferent investigators. Burmeister and Hartmann described a proboscis, while Claus 



