REACTION AND RESISTANCE OF FISHES. 



247 



day. Table IV. inserted below, is made up from a combination 

 of the data found in the two tables; most of the data in Table 

 IV. refer to the three lakes in question. In the instance of 

 Triarthra, however, the data come from two other lakes, as this 

 form does not occur in the three lakes from which the other 

 data are taken. 



TABLE IV. 



SHOWING THE RELATION OF ZOOPLANKTON TO NEUTRALITY. 

 The table is compiled from Birge and Juday's ('12) Tables XVIII and XIX, 

 Most of the data are taken from their records for the three lakes, Canandaigua, 

 Seneca, and Skaneateles. In these lakes the neutral depth was accurately located 

 by titration of samples. The titrations and plankton collections were made on 

 the same say. The data for the rotifer triarthra are taken from lakes Hemlock 

 and Keuka as these are the only lakes in which this form occurs in the records, 

 n.c. = no collection at this degree of acidity or alkalinity. The figures in the 

 columns indicate the number of forms per cubic meter of water. 



Letters in parenthesis after name of animal indicate the following. 

 Rotifer; (P) = Protozoan; (C) = Cladoceran; (Co) = Copepod. 



(R) = 



Table IV. shows (i) that all the zooplankton forms are more 

 numerous on either the acid or the alkaline side of neutrality, 

 than they are at neutrality itself, i. e., they are negative to neu- 

 trality; (2) some forms as Pleosoma and Vorticella, are found 

 only in the alkaline water; (3) others range between slight alka- 

 linity and slight acidity but are never very numerous at neu- 

 trality and often (Daphnia, Ceratium, etc.) show an increase 

 on either side; (4) a few forms (Triarthra) occur wholly on the 

 acid side of neutrality. 



