ON SOME POINTS IN THE STRUCTURE OF THE LARVA 
OF EPISCHURA LACUSTRIS ForUes. 
BY C. DWIGHT MARSH, 
Professor of Biology in Ripon College. 
WITH PLATES XII AND XIII. 
Epischura is a genus of copepods found only in America, its 
nearest European relative being Reterocope , and is remarkable 
for the very pronounced asymmetry of the abdomen. This is 
especially noticeable in the male of Epischura lacustris Forbes, 
in which not only is the abdomen twisted to the right, but cer¬ 
tain of the segments have marked lateral projections which to¬ 
gether form a complicated grasping organ. 
Inasmuch as Epischura is a form peculiar to America, and 
yet with no nearly allied forms in this country, its larval his¬ 
tory is a matter of considerable interest as being likely to 
throw some light on its relationship to other copepods. 
Forbes (’91, “ On some Lake Superior Entomostraca ”) says, 
“ among the many hundreds of specimens which I have exam¬ 
ined from the Great Lakes and from several of the smaller lakes 
of Illinois, Michigan, and Wisconsin, I have rarely seen an im¬ 
mature form. ” It is true that during the summer months, when 
one is most likely to make collections of entomostraca, larval 
forms of Epischura are very rare, although I have found them 
in certain localities in May and even in August. It is in the 
winter months, however, that they are found in the greatest 
numbers, especially in the month of March. I have collected 
from Green Lake a large amount of material illustrating the 
larval stages, and I hope, later, to make a fairly complete de¬ 
scription of its development. The publication of the results will 
necessarily be long delayed because of the time consuming labor 
involved in making the extremely delicate dissections of these 
