niATO!\I :\IOTTON. 



131 



FiGURK II. J^cv/ Heurckia rliomboides, Breb. 



POSITION TIMK 



2 7.16 Motion reversed. 



3 7-i6^-2 



4 7.17 Motion reversed. 



5 7.18 Diatom turned on its posterior end at X, 



6 7.18'- and reversed its motion at 5. 



7 7.20 



8 7. 20 ',4 Passed from view. 



