70 EVENINGS AT THE MICKOSCOPE. 



Avill just point out a beautiful though minute proof of 

 design in a point of the structure of the cells connected 

 with these pearly chambers. If you look closely, you 

 ■will see that the spines of the margin are not found on 

 those cells that- carry the pearls ; and moreover, that 

 they are also wanting on the approximate edges of the 

 two cells that lie behind every such pearl-bearing cell. 

 Now the reason of this omission is obvious. The spines 







iSSS- 



LEAFY i I V-M i I 



(A portion ii _ i' 



projecting obliquely would interfere with the gaping of 

 tlie door ; and hence they are invariably absent there. 



I happen to have in my aquarium a living individ- 

 ual of another species belonging to the same class, and 

 agreeing with this in all essential particulars of struc- 

 ture, though widely different in form. The difference, 

 however, is mainly dependent on a rather imimportant 

 point of arrangement ; for the cells, instead of being set 

 side by side and end to end in quincunx fashion, to an 

 indefinite extent, on two surfaces of a plane, are dis- 

 posed on one single surface, and in longitudinal rows 



