1883.1 Zoology. 209 



Claus, Dana, Leydig, Jurine, Baird, Fischer, Miiller, Lubbock, 

 Boeck, Brady, Heller, Lilljeborg, Sars, Uljanin, etc. As yet, how- 

 ever, it is too soon to say how far this similarity may extend. 



Confining ourselves, for the present, to fresh-water forms, a recent 

 opportunity for comparison of American with European Copepoda 

 has confirmed our impression that a large number of species will 

 be found identical^ It seems, indeed, somewhat astonishing at first 

 to discover that the isolated pools of the Central United States con- 

 tain species identical in every particular with those of England, 

 Scandinavia or Germany, but such is ' certainly the case. In fact 

 the populous genus Cyclops has few new species in America rela- 

 tive to the number identical with transatlantic forms. 



A Diaptomus, believed to be identical with D. castor in typical 

 as well as several varietal forms, occurs throughout Minnesota from 

 the shores of Lake Superior to near its southern boundary and in 

 Illinois. Another species believed to be nearly allied to a Scandi- 

 navian species is known from Minnesota, Wisconsin and the neigh- 

 borhood of East St. Louis, Illinois. Cylops serrulatus Cls., with 

 similar variations to those noticed by Claus (Op. cit, p. 85) and 

 Brady (Op. cit, vol. i, plate 22) occurs as our most abundant 

 species. 



It may be observed that Brady's work is so strictly systematic 

 that his figures are frequently little more than schematic, and lack 

 the life-like character of those in the earlier work of Claus. It 

 would seem that some of the species of Cyclops described by Dana^ 

 are identical with the above, although details are wanting to identify 

 positively. Without delaying to discuss the question opened as to 

 whether these widely separated forms have all diverged from a 

 primitive geographical center or have arisen independently from 

 original marine prototypes, as suggested to the writer by Professor 

 Leuckart, we may remark that the former theory is rendered pos- 

 sible by the fact that the feathers of water- fowl often form a vehicle 

 for the transportation of even larger Crustacea. 



Amphipods, for example, are transported hundreds of miles under 

 the feathers of geese. While it is unlikely that these larger crus- 

 taceans or their eggs would survive a long aerial journey, it is 

 quite certain that the eggs of Cyclops would pass many hours or 

 even days without being destroyed. On the other hand, it seems 

 that some entomostraca are in a nascent condition which permits 

 a slight change in the environment to induce remarkable altera- 

 tions in structure which are uniform wherever this change is 

 effected^ and if this be not now the case with all, it may have been 

 so at one time with the prototypes of our fresh-water copepods. 



To return to the question of heterogenesis. Selecting the larger 



^ Herrick : Copepoda of Minnesota. Rep. Geo]. Surv. Minn. 1881. 

 ^ J. D. Dana; Wilke's Exploring Exp. Crustacea. 



^Siebold and KoUiker, Zeilschrift. 1872, p. 293. Packard; synopsis of Phyllo- 

 pod crust. N. A. U. S. Geol. and Geog. Surv, of Col. 1873. ?• ^H* t;tc. 



