702 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [2] 



from Lake Michigan, mention of a single doubtful form in De Kay's Zo- 

 ology of New York,* and a brief article on "Fish Parasites" by Dr. 

 Kellicott. t 



In preparing the present notes I have had particularly in mind, be- 

 sides mere discrimination and description, the biological relations of 

 the species, as dependent on their situations and relative abundance ; 

 the origin of the Great Lake fauna, whether immediately and especially 

 marine or common with that of the Northern lakes at large ; and the 

 phenomena of the evolution of species in some of the more intricately 

 related groups. 



This subject has also its important economic relation. A thorough 

 examination of the minute life of the Great Lakes, with special reference 

 to the distribution, numbers and habits of the species of Entomostraca 

 occurring there, would greatly assist in the solution of some of the diffi- 

 cult problems of practical fish culture. Since it is now demonstrated 

 that our most important fishes are almost wholly dependent, at a criti- 

 cal period of their lives, on a sufficient supply of these small crusta- 

 ceans, these furnishing to fishes the first food they eat, and continuing 

 for some time to be substantially their only food resource, a knowledge 

 of these little creatures is scarcely less important to the scientific fish 

 culturist than a knowledge of fishes themselves. 



Order COPE POD A. 

 Family Calanidje. 



Diaptomus sicilis Forbes (Plate i, fig. G). 



D. sicilis, Forbes. Am. Nat., xvi (1882), pp. 541 (July), 645 (Aug.). 



D. pallidus, var. sicilis, Hcrrick. Fiual report on the Crustacea of Minnesota 



included in the orders Cladocera and Copepoda (in 12th Ann. Rep. Geol. 



and Nat. Hist. Surv. Minn. (1883), p. 137). 

 D. sicilis Underwood. Bull. 111. State Lab. Nat. Hist., n, 1886, p. 329. 



This beautiful species, a model of elegance and symmetry, is perhaps 

 the most abundant eutomostracan in my Lake Superior collections — 

 relatively much more common than in the southern waters of Lake 

 Michigan. It is closely similar to D. gracilis Sars (a common species of 

 clear lakes in Europe, from northern Italy J to Finland and Scandina- 

 via), but the constancy of the characters which distinguish it warrants 

 its separation. Although it is a decidedly variable form, its observed 

 variations do not appear to include or sensibly approximate the char- 

 acters of gracilis. The two have evidently had a common origin, not very 

 remote ; but their present geographical separation, shown by the con- 

 stancy of their differences, makes it altogether probable that this origin 

 dates from a time when communication between the fresh waters of the 



* Part vi, lt Crustacea," p. 62. 



t " On Certain Crustacea Parasitic on Fishes from the Great Lakes. Proc. Amer. 

 Soc. of Microecopists," i, pp. 53-57; 



1 1 in i u>r. 



