106 The First Food of the Common White -Fish. 



wide. Tlie 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 IJtaptomus 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 Limuocalanus was a much larger form, evidently 

 preying, to a considerable extent, upon the two just mentioned. 

 All the Cladocera noticed were Uaphnia hyalina., an elegant 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, Limuocalanus 7, Daphnia 3, and 

 Chironomus larva? 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 Limuocalanus; 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- 



