438 Birge — Vertical Distribution of Pelagic Crustacea. 



and 3 p. m. of the 27th, and 12 m. and 9 a. m. of the 28th r 

 The maximum temperature of the air was 33.3° C. (92° F.) 

 on July 27 and 30° C. (86.2° F.) on July 28. The minimum tem- 

 peratures were 23.2° (73.8° F.) and 21° (69.9° F.) respectively. 

 The temperature of the surface ranged from 18° at night to 

 20°-22° C. in the middle of the day. The wind in this case 

 blew from the nearer shore, the buoy being placed not quite a 

 half mile from the southern shore of the lake. The nights were 

 dark, somewhat hazy and cloudy. This period and the fourth 

 would have been made longer except that it became plain that 

 the distribution of the Crustacea was essentially the same as in 

 Period II. 



In the fourth period, extending from 6 a. m. of August 1, 

 to 9 a. m. of August 4, the wind was in the north and north- 

 west, and was so heavy as to interfere with observations. No 

 observations were made after 9 a. m. of August 2 until 9 a. m. 

 of August 3. The wind at this time was not too heavy to per- 

 mit a large boat to go upon the lake, but as our observations 

 were made from a rowboat, it was impossible to make them 

 when even a moderately strong wind was blowing from the 

 north. The temperature reached a maximum of 31° C. (88° F.) 

 on the 1st of August, and of 21° (70.5° F.) on the 3rd, with a 

 minimum of 20° (69° F.) on August 4 and of 8.8 Q (47.9° F.) 

 on August 3. The effect of the long continued and somewhat 

 heavy north wind was apparently to distribute the Crustacea 

 over a greater depth. It will be seen from the tables that the 

 average catch for the 9-12 m. level was considerably increased. 

 Below 12 m. the wind had no appreciable effect. During this 

 period the nights were dark. 



It thus appears that the last three sets of observations 

 covered a great range of meteorological conditions. In Period 

 II the weather was calm and bright and the nights were 

 moonlight. In Period III the wind was from the south, the 

 weather the ordinary summer weather, and the nights dark. In 

 Period IV the weather was distinctly cool, the wind was from 

 tne north, and the sky in both of the later periods was somewhat 

 ciouded. With the exception of the influence of the wind, of 

 which mention has been made, no effect upon the distribution of 



