PLATE XXVII. 



Figures magnified oOO diameters. 



Page. 

 Aethodesmds Incus, large form, ■ ■ • ^^^ 



" " smaller form, . ^104 



" " long spined variety, 104 



'• " depressed variety, • 1''* 



" " quadrate variety, 1"4 



'• " quadrate variety, smaller, 104 



" " creoate-cuneate, '. ■ 104 



" " two cells conjugating, 104 



'■ " zygospores doveloped, . 104 



" " end view of cell, 104 



Figs. 11, 12. Arthrodesmtis STJEULATUS, front and end view, 104 



" 1 3, 14. Arthrodesmus ovalis, front and end view, 103 



" 1.5, 16. Arthrodesmus orbicularis, front end view, . 104 



" 17, 18. Akthrodesmus quadridens, front and end view, . 104 



" 19, 20. Arthrodesmus octocorstis, Var. twin spined, 104 



•' 21-23. " " larger and smaller typical form, 104 



Fig. 24. COSMARIUM suborculare, . . ■ .85 



" 25. Desmidum cylisbricum, (Compare Plate III, fig. 1,) to illus- 



trate the division of " cell in the 

 process of growth, . . 26 



" 26. Hyalotheca DissiMENS, (Compare Plate I, figs. 4, 5, etc.), the 



middle cell is normal, the other two 

 enlarging preparatory to division in 

 the process of growth, 22 



" 27. CosMARiUM BoTRYTis, two cells, opening on one side, putting 



forth cytioplasm, uniting, thus perform- 

 ing the first act of conjugation, 81 

 " 28. The whole contents, cytioplasm, of the cells, poured out com- 

 mingled and formed into the zygospore, . 1 9 

 " 29. The tubercles on the membrane formed around the tnass of 

 cytioplasm (fig. 28,) developed into spines. Iii the process of 

 further development the membrane breaks, lets out some of the 

 cytioplasm ; (fig. 29,) this assumes a spherical form, (fig. 30,) 

 membrane increases in thickness and number of layers ; the 

 contents divide in one direction, (fig. 31,) then subdivided in 

 a transverse direction, (fig. 32). Two or four daughter cells 

 are thus formed in all respects like the mother cell, except in 

 the granules of the membrane ; these develop later, 1 H 

 •' 33. A cyst containing a number of small Closteriums ; supposed to 



be the development of a zygospore by another process, 1 9 



