NO. 1783. NORTH AMERICAN LERNJEOPODID.'E— WILSON. 211 



incomplete condition of the mouth-parts, indicate strongly that this 

 is a sliprt transition period, just long enough to bring larva and host 

 together. 



The present species infests the Centrarchidse, and fishermen are 

 well aware that these fish are m the habit of catching their food at or 

 near the surface of the water. And this is the place where the 

 xichtheres larva awaits its victim. In seizing its prey, as well as in 

 the act of ordinary breathing, a fish takes in water through its mouth 

 and expels it through the gills. The Aclitheres larva would be easily 

 swept in at such a time by the incurrent water, and when brought in 

 contact with the gills by the outcurrent its powerful grasping organs 

 would enable it to secure a firm hold on the gill filaments or arches. 



It is worthy of notice in this connection that those of the 

 Centrarchidse which feed most persistently at the surface are the 

 very ones most infested by these parasites. The red-eye, Ambloplites 

 rupestris, is the common host of the present species. 



FIXATION TO THE HOST. 



Of course, it is practically impossible to actually witness tiie fasten- 

 ing of the larva. But from what has been observed in the chalimus 

 larva of the Caligidse,'^ we can infer what occurs here. The outer end 

 of the attachment filament is enlarged into the mushroom form already 

 described and is filled with adhesive fluid. It lies just inside the 

 frontal margin, covered only by the very thin outer cuticle (fig. 23) . 

 Doubtless, the larva rubs its frontal margin against the skin of the 

 gill arch of its host and in this way burrows through the slime and 

 outer integument to the solid tissue underneath, holding on mean- 

 while with its powerful maxillipeds. At the same time the thin 

 covering of the frontal margin of the parasite is broken through and 

 the end of the filament is brought in contact with the gill arch, to 

 which it adheres firmly. By moving away from the point of attach- 

 ment, the coiled filament is drawn out of the body of the larva. As 

 it comes forth the larva grasps it between the claws at the tips of 

 the second maxillae. These claws are bent into a half circle whose 

 diameter is one-half larger than that of the filament. The latter can 

 thus slip through the claws easily, but by shutting past each other, as 

 they naturally do, the claws can still retain a firm hold. When the 

 enlarged posterior end of the filament is reached, it is held securely 

 between the claws and is removed entirely from the frontal margin. 

 The attachment filament thus becomes fastened to the ends of the 

 second maxillae, where it afterwards remains throughout life. 



That this transference of the filament from the frontal margin to 

 the tips of the second maxillae takes place at the time of fixation is 

 manifest from several considerations. 



a Proc. V. S. Nat. Mus., vol. 28, p. 546. 



