106 
The First Food of the Common White-Fish. 
wide. The next in size, and by far the most abundant member of 
this group was a Diaptomus, likewise new, described in the paper 
just cited under the name of Diaptomus sicilis. This appears in 
two forms, one evidently young in the stage just preceding the 
adult. Full grown individuals were .065 inch long, by one-fourth 
that depth. The Limnocalanus was a much larger form, evidently 
preying, to a considerable extent, upon the two just mentioned. 
All the Cladocera noticed were Daphnia hyalina , an elegaut and 
extremely transparent species, occurring likewise in the lakes of 
Europe. A single insect larval form (Chironomus) should likewise 
be mentioned in this connection, since it had about the same size 
and consistence of the Entomostraca, and was consequently equally 
available for food. 
The specimens of each of the above species from a certain 
quantity of these collections were counted, in order to give a defi- 
nite idea of their relative abundance in the lake. The Diaptomus 
numbered 225, the Cyclops 75, Limnocalanus 7, Daphnia 8, and 
Chironomus larvae 1. It was a curious fact, however, that when 
the water was drawn off at the end of the experiment, more than 
half the Entomostraca were Limnocalanus; a fact partly to be ex- 
plained by the predaceous habit of the latter, and partly by the 
facts relating to the food of the fishes themselves, which are pres- 
ently to be detailed. 
The fry were placed in the tank and supplied with their first 
food on the evening of the 12th of March. On the 14th, one 
hundred specimens were removed, and twenty-seven of these were 
dissected. Twenty were empty, but the remaining seven had 
already taken food, all Cyclops or Diaptomus. Three had eaten 
Cyclops only, and six Diaptomus, while two had eaten both. 
Fourteen of these Entomostraca, seven of each genus, were taken 
by these seven fishes. From those captured the next day, twenty- 
five specimens were examined, of which nineteen were without 
food. Of the remaining six, three had eaten Diaptomus and three 
Cyclops; five of the former being taken in all, and ten of the lat- 
ter. Three specimens were next examined from those caught on 
the 19th of March, two of which had devoured Diaptomus, and a 
third a single Cyclops thomasi and a shelled rotifer, Anurcea striata. 
The character of the food at these earliest stages was so well set- 
tled by these observations that I deemed it unnecessary to exam- 
