68 EVENINGS AT THE MICROSCOPE. 



rows, each containing 28 cells, or thereabouts. Very 

 well ; a simple arithmetical process shows that there 

 are 1,680 cells in this square half-inch ; or 6,720 in a 

 square inch. Now this A'ery specimen, before I mutil- 

 ated 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 number ; and 

 thus you see that I have not exaggerated the population 

 of this tiny marine city. This, however, is by no means 

 a specimen of unusual size. 



These cells, which I compare to cradles, are of shal- 

 low depth, but the head-part rises to a much greater 

 height than the foot. All round this elevated portion 

 the margin is armed with short blunt spines, two on 

 each side, which stand obliquely erect, projecting out- 

 wards over the middle of the next cell, which thus, in 

 concert with the spines of the cell on the opposite side, 

 they protect. 



If you search carefully over the aggregation of cells 

 with this pocket-lens, you will perceive that on some of 

 them are seated minute white globules, which look like 

 tiny pearls. These are not placed in any i-egular order, 

 two being sometimes found on contiguous cells, but 

 generally they are scattered at more or less remote in- 

 tervals. If we now apply the microscope to these ap- 

 pendages, each globule is seen to be flat on that per- 

 pendicular side which faces the foot of the cradle ; and 

 this flat side is a movable door, with a hinge along its 

 lower edge. The door is of a yellow hue ; the globule 

 itself being, as I said, of a pearly white hue. 



This is all that we can see in this dried specimen ; 

 but if we had been fortunate enough to have examined 

 it when first it was torn from its attachment to an old 



