80 MICROSCOPY FOR BEGINNERS. 



/. Each beak about as long as the green body, some- 

 times shorter ; whole cell slightly curved, vacu- 

 oles usually indistinct. C. rostrdtum, Fig. 30. 



Fig. 30. Closterium rostiitum. 



f. Each beak extremely fine, longer than the spindle- 

 shaped green body, the tips alone curved. C. se- 

 taceum. Fig. 31. 



Fig. 31. Clost&'ium setacenm. 

 7. MICRASTERIAS (Figs. 32 to 39). 



Each Micrasterias is divided across the middle into 

 two equal and similar halves, or semi-cells, by a deep 

 slit, the sides of which may be either close together 

 or somewhat separated. Both semi-cells are also very 

 much slit and notched, but both in the same way, the 

 description of one half, therefore, applying equally well 

 to the other. There are forty-two species of the genus. 

 The beginner must expect to find many forms not in- 

 cluded in this list, which contains only some of the most 

 common in the writer's vicinity. 



Some Species of Jtficrasterias. 



1. More or less circular in outline (a). 



2. Not circular ; divided into radiating arms (5). 



3. Not circular ; not divided into arms ; central slit 



gaping 0). 



