OXE TEXT FIGURE AND TWO PLATES (TWELVE FIGURES)
Phylogenetically tlie polyclads occupy an interesting and somewhat ambiguous position. Yet, both from an absolute and a relative standpoint, surprisingly little attention has been paid to tlie details of the central nervous system in this group. Among the few investigators who have interested themselves in the polyclad nervous system, the majority (as, for example, Bock, '13 ; Reisinger, '25 ; Steinbock, '25) hare laid emphasis on details of arrangement of the peripheral nerves and the nerve nets. Save for the early general studies of Lang (1879, 1881, 1884) and the later more detailed investigation of Stylochoplana maculata and Notoplana atomata by Hadenfeldt ( '29) there are practically no data concerning the organization of the central nervous system itself. None of the earlier workers mas able to obtain satisfactory silver impregnations.
I n the present work an attempt has been made to ascertain which features appear to be common among the polyclads as well as which features appear to be variable, in the hope that the status of this group with regard to the evolution of tlic nervous system may eventually be evaluated.
Methods
All specimens of Leptoplana acticola Boone ('29) were collected at Moss Beach, California. Three fixing solutions