547 



Further, the marshes and shallower lakes are the favorite breeding 

 grounds of fishes, which migrate to them in spawning time if possible, 

 and it is from the Entom.ostraca found here that most young fishes get 

 their earliest food supplies — a danger from which the deep-water species 

 are measurably free. Not only is a high reproductive rate rendered un- 

 necessary among the latter by their freedom from many dangers to which 

 the shallow-water species are exposed, but in view of the relatively 

 small amount of food available for them, a high rate of multiplication 

 would be a positive injury, and could result only in wholesale starvation. 



All these lakes of Illinois and Wisconsin, together with the much 

 larger Lake Mendota at Madison (in which also I have done much work 

 with dredge, trawl, and seine), differ in one notable particular both 

 from Lake Michigan and from the larger lakes of Europe. In the latter 

 the bottoms in the deeper parts yield a peculiar assemblage of animal 

 forms which range but rarely into the littoral region, while in our inland 

 lakes no such deep water fauna occurs, with the exception of the cisco 

 and the large red Chironomus larva. At Grand Traverse Bay, in Lake 

 Michigan, I found at a depth of one hundred fathoms a very odd fish 

 of the sculpin family (Triglopsis thompsoni Gir.) which, until I collected 

 it, had been known only from the stomachs of fishes ; and there also 

 was an abundant crustacean, Mysis — the "opossum shrimp", as it is 

 sometimes called — the principal food of these deep lake sculpins. Two 

 remarkable amphipod crustaceans also belong in a peculiar way to this 

 deep water. In the European lakes the same Mysis occurs in the 

 deepest part, with several other forms not represented in our collections. 

 two of these being blind crustaceans related to those which in this country 

 occur in caves and wells. 



Comparing the other features of our lake fauna with that of Europe, 

 we find a surprising number of Entomostraca identical ; but this is a 

 general phenomenon, as many of the more abundant Cladoccra and Co- 

 pepoda of our small wayside pools are either European species, or differ 

 from them so slightly that it is doubtful if they ought to he called dis- 

 tinct. , 



It would be quite impossible, within reasonable limits, to go into 

 details respecting the organic relations of the animals of these waters, and 

 I will content myself with two or three illustrations. As one example 

 of the varied and far-reaching relations into which the animals of a lake 

 are brought in the general struggle for life, I take the common black 

 bass. In the dietary of this fish I find, at different ages of the individual, 

 fishes of great variety, representing all the important orders of that 

 class ; insects in considerable number, especially the various water-bugs 

 and larvae of day-flies ; fresh-water shrimps ; and a great multitude of 

 Entomostraca of many species and genera. The fish is therefore direct- 

 Iv dependent upon all these classes for its existence. Next, looking to 

 the food of the species which the bass has eaten, and upon which it is 

 therefore indirectly dependent, I find that one kind of the fishes taken 

 feeds upon mud, algae, and Entomostraca, and another upon nearly every 



