16 R. LUNDBERG, DEVELOPMENT OF THE DAPHNIDS. 



ting the faciilt}' of the water to keep small particles in a 

 suspended state. Althoug-li this influence can not be so great 

 upon the organic plankton as upon tlie inorganic silt (»pons- 

 siéres en suspension ). temperature. light and the density of 

 the water must have an essential influence even u})on higher 

 organisms, provided with the faculty of moving about by 

 themselves, as do the pelagic or limnetic Cladocera. and still 

 more upon the niicroorganisms vvhich constitute the food foi- 

 the others. This ean not be stndied so fa\ourably in lakes 

 as in the open sea. where in siunmertime the temperature 

 is subject to greater variations. Dr L. Kolmodin •") has 

 made such investigations in the Baltie for the practical 

 purpose of tinding to vvhat depth the drift-net for eatching 

 herrings ought to be sunk. These investigations show very 

 plainly, that the distribution of the entomostraca in strata 

 of dilferent depths is inilueneed to a great extent by the 

 temperature. I believe that such, and other more exclusively 

 scientific investigations can be of the greatest importance 

 for the explanation of the causes of the very iuteresting 

 transformatious of Cladocera. since 1 do not consider the 

 \'ariation alone to be the right explanation. 



The remark may be made, that such transformatious during 

 the growth oocurs also in the Daphnids which only live in 

 shallow water. where in summertime the temperature is just 

 about the same from the surface to the bottom. This is true, 

 but liere it might ha^•e a phylogenetical explanation, which 

 is the more likely as the pelagic forms are in phylogenetical 

 respect older, as Weismann '") has already noted about Lcpto- 

 dora hl/al hl a. 



