220 Marsh—Limnetic Crustacea of Green Lake. 
where the numbers of a species were very large, would the fact 
that a considerably larger number were found in one collection 
than in another be any conclusive argument against the practi¬ 
cal uniformity of distribution. Nor, on the other hand should 
it be assumed, because two or three successive hauls show the 
same, or nearly the same numbers, that the distribution is 
therefore uniform, because this could be easily explained by sup¬ 
posing that the swarm was of considerable extent or remained 
stationary for a considerable period. 
My collections made in 1893, which were reported in the for¬ 
mer paper, were made almost continuously in the course of two 
days. Now if the plankton is uniformly distributed, those collec¬ 
tions should show a practical uniformity of numbers, and 
the more numerous a species was, the less should be the pro¬ 
portional variation. Yet the collections of Diaptomus , the most 
abundant genus, varied from 291 to 2,966. In many of the col¬ 
lections made in the fall of 1894 on the same day, or successive 
days, there was a marked uniformity in the numbers of Diaptomus , 
as for example, nos. 4.94, 5.94 and 6.94 show a range of num¬ 
bers only from 4,171 to 5,630. If one were to base his conclu¬ 
sions on a small number of observations, he might well say that 
here was clear evidence of uniformity. Yet a few hours later in 
the same place I found only 2,023; with a difference as great as 
this, we certainly cannot speak of the Diaptomi as being uniform¬ 
ly distributed. In hauls 21.94 and 22.94, made in the forenoon 
of October 25, there was in one case 1,917 and in the other 
3,823 — twice as many. Still more marked was the difference 
in two collections, one made at about six p. m., and the other 
between ten and eleven p. m., November 8. In the six o’clock 
collection there were 884, while in the evening collection there 
were 6,447. Such an enormous difference as this is certainly 
not consistent with any theory of uniformity of distribution. In 
these same two collections of November 8, Cyclops fluviatilis 
showed a similar wide variation,— the numbers in the six o’clock 
collection being 1,912, and in the evening collection being 564. 
October 24 I found between ten and eleven o’clock in the even¬ 
ing 1,241 C. fluviatilis, and yet the next morning between six 
and seven o’clock, I found only 618. 
