124 CLAUDE W. MITCHELL 



darum auch eine Korrelation zwischen der jahrlichen Variations- 

 kurve der Grosse des Panzers und der jahrlichen Temperaturkurve 

 erwarten. 



May it not be well at least to point out that the correlation 

 which Lauterborn has shown to exist between the temperature of 

 the water, and the form, size, and so forth, of Anuraea may quite 

 as well be an indirect as a direct relation. We believe that no- 

 where in his article does Lauterborn consider the question of the 

 feeding habits of the organism which he has studied so exten- 

 sively ; yet nothing would seem more natural than that a change 

 in thermic conditions may ^ive rise to changed and varied food 

 supplies, which in their turn may modify Anuraea as we have 

 found such changes to modify Asplanchna. If observation 

 or experiment should show this latter supposition to be correct, 

 we should at once have an explanation for certain facts which, 

 as Lauterborn himself states, are not explicable upon the hypoth- 

 esis of direct influence of temperature. These facts are, namely, 

 that with the advent of spring there appears in Anurea not one 

 line of mutation or line of variation, but instead, several definite 

 lines diverge simultaneously. Such results may not be in con- 

 tradiction to the theory of direct effect of temperature but the}^ 

 at least seem more in harmony with the assumption of \'aried 

 habits of feeding as the definite causes of the changes. 



Victor Langhans and Wesenberg-Lund have also made inter- 

 esting observations upon marked variations which occur in 

 Asplanchna priodonta. Their observations are essentially sim- 

 ilar though their interpretations differ. This species is a fairly 

 close relative of the species which we have studied. The facts 

 recorded are essentially as follows: The size of the species 

 varied enormously. One form, which is spherical and found 

 only in winter, is about one-third as large as the huge elongated 

 summer form. The jaws (Langhans), though of the same gen- 

 eral type, differ in many minor respects. Since the appearance 

 of these types follows definite seasons of the year, Wesenberg- 

 Lund ('98) at first concludes that the variation depended upon 

 internal factors. To quote, he says (p. 209) : 



