129 



desert the upper meter or two on bright, sunny days and the other two 

 members occupy this region in rather limited numbers. But, on cloudy 

 days, all are foiuid in this region in nearly as large numbers as at night. 

 This seems to shoAV that light is the primary factor controlling their move- 

 ments. They move down to avoid intense light and then move up into 

 this region again as soon as the intensity of the light is sufficiently de- 

 creased. 



Epischura, Lcptodora, and Corethra larvre belong to the second group. 

 The depth to which these descend in the daytime did not depend, appar- 

 ently, upon the intensity of the sunlight as they were found at the same 

 depth on cloudj- as on clear days. Besides, it does not seem probable 

 that sunlight alone would cause them to descend to so great a depth, that 

 is, five to seven meters or more, especially since the transparency of the 

 water was so low, 2.1 to 2.5 meters. Therefore, it seems reasonable to 

 suppose that some other factors are verj- largely responsible for their 

 movements. 



Daplinla ptilicaria might also be added to this gi-oup. While it showeil 

 only a very slight tendency toward diurnal movement in Winona Lake, it 

 did show distinct and regular migrations in one of the Wisconsin lakes 

 upon which the writer made observations. In the latter lake the same as 

 in Winona Lake, it remained in and below the thermoeline in the daytime 

 and in neither case was its day position affected by the intensity of the 

 sunlight. In general, the diurnal migration of all the members of this 

 group, seems to be much more akin to the "nocturnal habits" of many 

 other animals, than are the movements exhibited by the members of the 

 first gi'oup. 



Some Crustacea upon which experiments have been performed, have 

 shown that they are attracted by diffuse light. If this were true of all 

 Crustacea, and if it were to hold true for them in their natural haunts 

 as well as in the laboratoi-y, then one might suppose that there would 

 be morning and evening surface increases of about equal proportions. 

 Furthermore, it would not be unreasonable, perhaps, to expect moonlight 

 to produce an appreciable effect, if the Crustacea were attracted by diffuse 

 light. For the most part, however, the truth of this supposition is not 

 confirmed by the Crustacea of Winona Lake. With the exception of the 

 young Daphnia hyalina in the second all-night series, there was no morn- 

 ing surface increase comparable in every way to that of the evening. 



9 — Academy of Science. 



