240 Proceedings of Indiana Academy of Science 
pair entered under the same number in my notes as was written upon 
the dish. 
I found that Hyalella would feed upon almost any water plant, but 
seemed to show a preference for certain ones such as Ceratophyllum, 
Elodea, and Chara. I also observed amphipods of the species feeding 
upon certain animal tissue, e.g. a dead dragon-fly nymph, a dead isopod, 
a dead amphipod, ete. Foods of other species of amphipods are dis- 
cussed in some detail, by Sexton and Mathews (713), M. Armand Viré 
(03), and Della Valle (’93). 
RELATION OF REPRODUCTION. TO SEASON. 
All the evidence that I have collected points to the fact that 
Hyalella has a distinct breeding period, limited to the warmer months. 
For example, when a hundred or so animals were examined during the 
first of February, not a single female was found with eggs in the brood 
pouch nor were there any young, present. The same was true when 
several hundred adults were examined the first of April. At neither 
time were any individuals observed mating when they were brought to 
the laboratory, but the second day after they were collected and in a 
warm room some fifty-odd pairs were isolated, the male carrying the 
female in the usual manner when preparing for copulation. These ani- 
mals were collected on April 6, and on April 8 were noticed pairing. 
This sudden change in so many animals shows conclusively that both 
sexes were ripe and ready for mating as soon as conditions (which I 
believe to be temperature) were suitable, but the time for mating was 
put off as long as conditions were not favorable. All the females, 
whether mated or not, could be easily distinguished from the males, 
because the ova could be distinctly seen and approximately counted as 
they lay in the ovary which is located in the dorsal thoracic region. 
The testes appeared as a lighter green than the ovaries and are located 
approximately in the same position in the male as the ovaries are located 
in the female. The testes, however, were much more elongated, tapering 
at each end while the ovaries appeared as a cylindrical green patch end- 
ing abruptly at each end. The male ducts according to Kunkel (718) open 
by papillae on the ventral side of the last thoracic segment. The ovi- 
ducts each open at the base of the fifth coxal plate so that when the 
eggs are deposited they are caught in the marsupium which is formed 
by certain hair-like projections on the ventral side known as oostegites. 
Fifty pairs were isolated the day the male began to carry the fe- 
male. Of these I succeeded in carrying only three pairs through to the 
second oviposition. These were pairs 6, 9, and IV, Table 1. In two 
cases there were twenty-four days and in one case twenty-six days 
between two successive ovipositions. The dates are found in Table 1. 
The young (Table 2) hatch about the twenty-first or twenty-second 
day after oviposition and remain in the brood pouch from 0-3 days 
when they are extruded at the time the moult of the female occurs in 
preparation for the next oviposition. The male may begin to carry the 
female as early as the seventh day before she moults, three or four 
days before the young are even hatched. The eggs become easily 
visible about a week before they are laid. Jackson (’12) succeeded in 
