120 



desert the upper meter or two on liriglit, sunny d:iYS and the otlier two 

 menil)ers occupy this region in ratlier linuti'd nund)ers. But, on cloudy 

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

 This seems to show that light is the pi-imary factor controlling their move- 

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

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

 creased. 



EpiKcJiiird. Li'itfndord. and ContJird larva^ 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 fouiul at the same 

 depth on cloudy as on clear days. Itesides. it does not seem prol)able 

 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, IM lo 2..") meters. Therefore, it seems reasonable to 

 suppose that some other factors are very largely responsil)le for their 

 movements. 



Ddliluiid inilii-iirid miglii also lie added to this group. Wliile it sliowed 

 only a very slight tendiMicy foward diurnal movement in Winona Lake, it 

 did shoAv distinct and i-egidar nngrations in one of the Wisconsin lakes 

 upon wliich (lie wi'itci' made observations. In tlie latter lake the same as 

 in AVinoii;! Lake, it remained in and below the thernioclinc in the daytime 

 and in neither case wa>; its day jiosition affected by the intensity of the 

 sunliglit. In general, tlie diuni.il migration of :dl tlie members of this 

 group, seems to be mucli more akin to the "noclurnal habits" of many 

 other animals, th;in are the uiovements (exhibited 1iy the )iieml)ers of the 

 tirst groiip. 



Some Crustacea upon whicli exp(>riments have been performed, liave 

 shown that they are ;ittr;icred liy diffuse light. If this were true of all 

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

 as well as in tlie lalxn-atdry. tlu'U one might suppose that there would 

 be morning and evening siu'face increases of about equal proportions. 

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

 to pi'oduce an appreciable effect, if the Crustacea were attracted l)y 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 Ddliluiid Injdlidd in the second all-night series, there was no morn- 

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



9 — Academy of Science. 



