Lake Maxinkiickee, Physical and Biological Survey 305 



Here among the algse, therefore, we should look for the chief 

 enemies of the leeches, and this period immediately after hatching 

 must constitute a critical period in their lives. 



There are two groups of animals which frequent the alg^e, both 

 of which probably eat many of the young leeches, although unfortu- 

 nately there is no direct proof of such a fact in the observations 

 here recorded. The importance of the leeches was not realized 

 until the very close of the summer's work and it was then impos- 

 sible to secure the evidence. 



The first is the group of small fishes called darters, that live 

 and breed amid the algae. In the few whose stomachs were ex- 

 amined were found the larvae of many animals that breed in the 

 algse and of some parasites (see p. 300). There is good reason 

 to believe that further investigation of the food of these fishes 

 would show that they occasionally eat leeches also. 



The second group is even more promising; it is the dragon-fly 

 nymphs whose greed and voracity are only too well known. 



They seize and devour everything in sight, and it must happen 

 sometimes that they get hold of leeches amongst their other prey. 

 At least there is promise enough in these two groups to warrant a 

 careful study in the future. 



The fishes get back at the leeches in another way also, since 

 the latter are often found in the fish's stomach mingled with other 

 food. Marshall and Gilbert, in their "Notes on the Food and 

 Parasites of some fresh-water Fishes from the Lakes at Madison, 

 Wisconsin" (Appendix to the Report of the Commissioner of Fish- 

 eries for 1904, pp. 513-532) record leeches amongst the food of 

 Esox lucius, Lepomis pallidus, and Mic7'opterus salmoides. 



That they are eaten by other fish also seems probable from the 

 testimony of City Marshal Fisher of Culver, who says they make 

 the best fish bait he ever tried. All sorts of fish bite at them 

 eagerly, bass, perch, bluegills, sunfish, etc. They are tough, so the 

 fish cannot tear them from the hook easily, and often two or more 

 fish can be caught with the same bait. 



Here is a good suggestion for the fishermen, especially when 

 other bait is scarce, and one that will help to rid the fish of their 

 worst enemy. 



Copepod Parasites 



The Copepod Parasites will be found fully treated in connec- 

 tion with the other Crustaceans, pp. 717-720. 



