PLATE I. 



Figures magnified 500 diameters. 



Fig. 1. SURIRELLA ELEGANS, showing the single nucleus and the 



radial distribution of the endochrome. 



" 2. SURIRELLA SPLEXVIDA, showing the two nuclei and the ger- 



minal (?) dot. Also the distribution of the endochrome in 

 the canalicnli and the arrangement of the lobes of the en- 

 dochrome with regard to the germinal (?) dot. 



Figs. 3, 4. The sporangium of the Surirella Splendida after the complete 

 fusion of the endochrome; the valves of the parent frus- 

 tules adhering. 



5, 6. SURIRELLA SPLENDIDA, early stage of conjugation; the fusion 

 of the two endochromes resulting in the enlargement of 

 the internal contents, and the separation of the valves of 

 the frustules which adhere to the mucous mass of the 

 sporangium. 



Fig. 7. EPITHKMIA VENTRICOSA, Thallus containing matured frus- 



tules and spores the same as are found in tlie diatom itself. 

 .s. Thallus containing several diatoms in early and later stages of 



development. 



9. Two diatoms fXavicula) conjugating and surrounded, by a 



gelatinous covering; the valves of frustule separated and 

 the endochrome contracted into spherical masses. 



Kigs. 10-12. CVMHELLA, phases of growth of the sporangium in its mucous 

 envelope. 



13. Process of division and multiplication of diatoms ; a X;ivicula ; 



F.F., the silicious epiderm ; <;.<}., the sides sliding one 

 over the other ; A., the nucleus; B.B.B., endorhroiiH 1 sur- 

 rounding the spojje or primordial cell ; D. D., central 

 cavities. 



14. A., the spores dividing and the end of the epiderm (F.F.) 



sliding apart. 



15. A. A., spore fully divided and the frustule separated by form- 



ing dividing membranes; thus there are two trust ales 

 approaching complete development. 



