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TJnivcrsiiy of California Fuhlications in Zoology. [Vol.4 



the ends of the horns and less abundantly on the thin ventral 

 plate (fig's. 5 and 6). The plasma streams out through these 

 pores (Sehiitt '99) in long filaments and may form an extramem- 

 branous sheet on the outer face of the exoskeleton. Both faces 



ap. p. 



r. ant. . 



Fig. 5. — Ventral view of Ceratium eugrammum, an anterior sehizont 

 after recent division. X 913. 



Fig. 6. — Dorsal view of the same. Eegenerated moiety of the theca 

 shown without pores. X 913. 



Abbreviations — ap. p., apical pore; f. p., flagellar pore; fis. J., fission 

 line; I. ant., left antapical; r. ant., right autapical; tr. f., transverse fur- 

 row; V. pi., ventral plate; l'-4', apical plates; l"-4", precingular plates; 

 1' "-5' ", posteingular plates; l""-2"", antapical plates. 



of the cellulose wall are thus accessible to action of the cytoplasm 

 in deposition or solution of the material of the wall. 



The thickness of the wall and the extent of its surface differ- 

 entiations in the form of lists, ribs, fins, and rugosities differ con- 

 siderably in different species, ranging from the thin hyaline, 



