Lake Maxinkuckee, Physical and Biological Survey 81 



particularly common on the Redeye and the Small-mouthed Black 

 Bass, two-thirds of the specimens examined being infested with this 

 parasite. Like the first species of Ergasilus mentioned above, it is 

 a family rather than a specifis parasite, as its name implies. This 

 species is as typically American as A. percariim is European, and 

 is fully as widely distributed. 



The life history of this species appeared in vol. 39, Proc. U. S. 

 Nat. Mus., pp. 194-224, pis. 29-36. 



Female Achtheres with ripe eggs were found toward the last 

 of August, and that may be designated as one of the breeding 

 seasons of the species.* The nauplius and metanauplius stages 

 are passed wholly inside the Qgg and the emerging larva is a fully 

 developed copepodid larva with an elliptical cephalothorax, three 

 free thorax segments, a two-jointed abdomen, and two pairs of 

 swimming legs. 



The most striking characteristic of this copepodid larva is its 

 attachment filament, which can be plainly seen inside the anterior 

 end of the body. This filament appears at the very beginning of 

 the nauplius stage; at first it consists of a large mushroom-shaped 

 body (the future button or disc) which is situated close to the 

 integument at the very anterior margin of the head, and a straight 

 stalk or filament passing directly backward from the center of 

 the disc. This filament is about one-fifth the diameter of the disc, 

 and its posterior end is slightly enlarged and fastened into the 

 tissue of the nauplius's body just back of the disc. As development 

 progresses the filament increases in length and begins to coil so 

 that just before the nauplius transforms into a metanauplius it 

 consists of two circular coils, one lying inside the other, the outer 

 one twice the diameter of the disc. In the free swimming cope- 

 podid stage there are three large coils instead of two. 



This larva shows only traces of a digestive canal, even under 

 the magnification, and the center of the body is still filled with 

 large yolk cells of different sizes. It swims about actively with 

 a motion like that of an adult Caligus, and at once seeks a host. 

 Like its European relative {A. percarum) it infests the Centrar- 

 chidse, and fishermen are well acquainted with the fact that our 

 game fishes belonging to that family are in the habit of catching 

 their food at or near the surface of the water. This is just where 

 the parasite larva is waiting for its host, and the two thus come to- 

 gether. All the larva needs is a chance to get inside the fish's 

 mouth without being swallowed, and such an opportunity is af- 



* For full account and figures see Proc. U. S. Nat. Mus., Vol. 39, pp. 189-226; pis. 29-36. 

 6— 17618— Vol. 2 



