LATTICE WORKERS, OR POLYCYSTINA. 89 



The method by which lime is deposited by the 

 animals of the Foraminifera, so as to construct their 

 calcareous shells, and that by which flint is collected, 

 in the allied group of Polycystina, for the elaboration 

 of their siliceous skeletons, appear to be the same in 

 both cases of all the essential points, although the 

 material is different. The structures are formed in 

 both by deposits at right angles to the principal 

 line of growth, and in one direction only. 1 Of course, 

 the material for this operation has to be derived from, 

 and is held in solution by, the water of the ocean, 

 whether it is to be regarded as a true secretion, or 

 merely an exudation, is a subtlety which need not 

 trouble us ; it is sufficient to remember that the de- 

 velopment and extrusion of the sarcoblast precedes 

 the first appearance of the embryonic skeleton. " All 

 subsequent deposits of silex, or flint, whether in the 

 shape of foraminated chambers, or spines, or other 

 portions of the structure, take place on the same 

 plan namely, by the deposit of silex at right angles 

 to the axis of growth, of the part immediately in 

 question. In the formation of the chambers the 

 deposit usually goes on from a number of points 

 simultaneously around the free margin, the points 



1 " Remarks on the Process of Mineral Deposit in the 

 Rhizopods," by, Dr. G. C. Wallich, in "Annals of Natural 

 History" (Jan. 1864), p. 72. 



