60 EVENINGS AT THE MICROSCOPE. 



^modern naturalists have given it the scientific appellation 

 of Flustra foliacea, and arranged it in the class Polt/zoa, 

 a group of animate beings, which have much of the form 

 of Polypes, and much of the structure of Mollusks. 



We cut off a little piece from the end of one of the 

 lobes, and put this upon the stage of the microscope. We 

 now see that the cells are disposed in nearly parallel rows ; 

 but so that those of one row alternate with those of the 

 next, quincunx fashion, the middle of one cell being 

 opposite the end of its right and left neighbours; or like 

 the meshes of a net. The cells extend over the whole leaf, 

 and are spread over both its surfaces in this case ; the 

 united depth of two cells constituting the thickness of the 

 leaf-like structure. There are other species, more delicate, 

 which have but a single series of cells, all opening on the 

 same side of the leaf. 



Each individual cell is shaped like a child's cradle; and 

 if you will imagine 20,000 wicker cradles stuck together 

 side by side in one plane, after the quincunx pattern I 

 have just mentioned ; and then the whole broad array 

 turned over, and 20,000 more glued on to these, bottom 

 to bottom, — you will have an idea of the framework of this 

 pale-brown leaf; dimensions of course, being out of the 

 consideration. The number may appear somewhat im- 

 mense, yet it is no larger than the ordinary average, as I 

 will soon show you. I measure off a square half-inch of 

 this leaf, which I carefully cut out with scissors; now with 

 the micrometer count the cells in the square piece. — You 

 find 60 longitudinal rows, each containing 28 cells, or 

 thereabouts. Very well ; a simple arithmetical process 

 shows that there are 1,680 cells in this square hal: inch ; 

 or 6,720 in a square inch. Now this very specimen, 

 before I mutilated it, contained an area of about three 

 square inches ; which would give 20,160 cells. This is 

 the number on one surface; the other contains an equal 

 aiumber ; and thus you see that I have not exaggerated 



