68 ETENINGS AT THE ISnCKOSCOPE. 



rows, eacli containing 28 colls, or thereabouts. Veiy 

 well ; a simple ai'itlimetical process sliows that there 

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

 square inch. Kow this very specimen, befoi'e 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 otlier contains an equal number ; and 

 thus 3'ou see that I have not exaggerated the population 

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

 a s])ecimen 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 tiian 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 ojiposite side, 

 they protect. 



If vou search cai-efuUy over the airgrefjation of cells 

 M'ith this pocket-lens, you will perceive tliat on some of 

 them are seated minute white globules, M-hicli look like 

 tiny ]icarls. Tlicse are not placed in any regular order, 

 two being sometimes found on contiguous cells, but 

 generally they are scattered at more or less remote in- 

 tervals. If we now aj^ply 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 pearh^ Avhite 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 fi'om its attachment to an old 



