340 



A. FRANKLIN SHULL. 



removed and promptly killed in Bouin's fluid. Other rotifers 

 from the same families were kept in ordinary water, under a bell 

 jar in air, for 24 hours, then killed in Bouin's fluid. 



The contraction of the foot muscles was noted in accordance 

 with the following arbitrarily chosen degrees of contraction: 

 (o) foot fully extended; (i) foot slightly contracted, toes bent to 

 one side, but still visible; (2) foot considerably contracted, toes 

 wholly concealed, but contraction limited to small region near 

 toes; and (3) foot greatly contracted, region of contraction much 

 greater than in preceding class. It is to be noted that this 

 classification is not the same as that proposed for the English 

 and Nebraska rotifers in my former paper (Shull, 1915). The 

 descriptions there given were not applicable to the rotifers used 

 in these experiments. 



The degrees of contraction of the foot muscles of the two lots 

 of rotifers is tabulated in Table V., and the statistical comparison 

 of the figures in Table VI. 



TABLE V. 



Showing the Degree of Contraction of the Foot Muscles of Rotifers Kept in Oxygenated 

 Water, and in Untreated Water, and Then Killed in Bouin's Fluid. 



TABLE VI. 



Statistical Comparison of Data in Table V. 



The statistical treatment is based on the assumption that each 

 degree of contraction of the foot muscles differs from the degrees 

 next to it by unity. 



As shown in Table VI. there is less contraction of the foot 



