82 Lake Maxinkuckee, Physical and Biological Survey 



forded in the ordinary act of breathing. Once inside the mouth 

 and swept against the gill-arches by the out-current of water, the 

 larva secures a firm hold by means of its powerful maxillipeds. 



It is noticeable in this connection that those of the Centrarch- 

 idse which feed most persistently at the surface are the ones in- 

 fested by this parasite. Even in the hottest weather the redeye 

 frequents the shallow water along the shore, at least at night. As 

 a result, its gills are practically certain to yield a goodly number of 

 Achtheres, and the same is true of the two kinds of black bass, 

 particularly the small-mouthed. 



On the other hand, a fish like the walleye, which frequents 

 deeper water, does not present as favorable an opportunity and 

 most of them are free from this parasite. 



Once fastened to the gill-arches, the parasite remains there for 

 life, so that the only chance its enemies have to kill it are while it 

 is swimming about freely at the surface. 



This free swimming period is much shorter than that of the 

 Ergasilus and Argulus larvae, but the Achtheres larva is larger than 

 the other two and so ofi'ers a more tempting bait. It is a signifi- 

 cant fact that so many of them were found in the stomachs of the 

 few minnows and darters that were examined. 



In this way they are kept within due bounds and prevented 

 from multiplying in sufficient numbers to become dangerous to the 

 larger fish. 



7. ACHTHERES MICROPTERI Wright 



Found on the gills of Micropterus salmoides and M. dolomieu. 

 This species is not at all common, and for a long time all the speci- 

 mens obtained from the two basses were supposed to belong to 

 the species ambloplitis. The female of this species, however, may 

 be distinguished from ambloplitis by the large abdomen with its 

 basal lobes and more distinct segmentation, and by the much 

 smaller egg-tubes. This distinction may then be confirmed by the 

 details of the mouth-parts. 



The male may be distinguished by its much larger size, and by 

 the chelae on the tips of the second maxillae. 



