76 Dr. G. C. Wallich on the Process of 



intermediate space, such as would necessarily exist were the 

 first two layers not secreted in contact. Hence it follows, that, 

 after the deposit of the two primary layers (by the surface of the 

 stolon and of the vacuolar cavity, as seen in fig. 2), all subsequent 

 layers must be evolved from these surfaces in opposite directions 

 —that is to say, centrifugally as regards the outer series, and 

 centripetally as regards the inner one. And it may be stated 

 that the growth of every sponge-spicule takes place in two oppo- 

 site directions between its axis and periphery, and that every 

 spicule presents an axial tube (or the remains of such tube), 

 which was originally occupied by the vacv,olar stolon around 

 which its several layers were deposited. 



I shall now endeavour to show that, with the exception of one 

 group of organisms which constitute the true connecting link 

 between the Sponges and the Rhizopods, the process of mineral 

 deposit in the latter class of Protozoa takes place so differently 

 from that just described as prevailing in the former, that it fur- 

 nishes a most important distinctive character between the two 

 classes. 



If we leave out of the question the genera Polytrema, Carpen- 

 teria, and Dujardinia, which are still sub judice, and restrict the 

 term " spicule " to structure identical in its mode of formation 

 with the spicules of the Sponges, no spicular growth has hi- 

 therto been met with amongst the Foraminifera. The point for 

 decision is not whether the spicules found in these genera are 

 true sponge-spicules (for of that fact there is no doubt), but how 

 they came there, — my argument being that, inasmuch as they are 

 undoubtedly true spicular growths, they cannot belong to, or be 

 formed by, Foraminifera, and must consequently be of ento- 

 zootic origin. 



Figure 5 is intended to illustrate the order in which the suc- 

 cessive layers of calcareous matter are formed in a shell of the 

 Globigerine type, p c representing the primordial chamber, 

 T T the first layer of shell secreted from the sarcode-surface with 

 which it is in contact ; s, s, s, pseudopodial stolons traversing the 

 shell through the larger foramina, and terminating at times, but 

 not necessarily always, in pseudopodia ; p, p, p, pseudopodia 

 taking their rise from an external layer of sarcode (or chitosarc, 

 to be described immediately), and, in like manner with the 

 pseudopodial prolongations of the stolons, not always in direct 

 communication with the sarcode-mass within the chambers; 

 and, lastly, a, the aperture of the chamber. 



s c represents the second chamber ; the letters t' t' the first 

 layer of shell, as in the primordial chamber ; s, s, the stolons, 

 with the large foramina for their exit ; p, p, p, pseudopodia, in 

 this case springing directly from the sarcode-mass of the cham- 



