92 PROCEEDINGS OP THE AMERICAN ACADEMY 



EXPLANATION OF FIGURES. 



ZONARIA VARIEGATA. 



Fig. 1. Small portion of edge of frond showing marginal cells. Surface view. 



X83. 

 Fig. 2. Vertical section near margin of the frond showing a well developed 



overlapping zone. X 200. 

 Fig. 3. Vertical section near margin of frond showing a very young stage in 



the development of overlapping zone. A indicates the direction of the 



margin, B indicates the direction of the base. 



m, medullary cell. 



c, cortical cell. 



m', divided medullary cells. 

 c', disintegrating cortical cells. 



d, remains of walls of cortical cells. X 350. 



Fig. 4. Same as Fig. 3, but older stage. 



ic, internal cortical layer, which is here pushed aside. X 350. 

 Fig. 6. Ehizoid-Iike hair. X 83. 



DiCTTOTA CILIATA. 



Fig. 6. Undeveloped tetraspore. X 200. 



Fig. 7. Tetraspore with two basal cells showing simple bisection. X 200. 



Fig. 8. Tetraspore showing radial divisions. X 200. 



Figs. 9 and 10. Irregularly divided tetraspores. X 200. 



All the figures were drawn with the aid of the camera lucida. From the 

 drawings thus made Figures 3, 4, and 5 were reduced one third ; the others 

 remain as they were drawn. 



