THE LIFE-HISTORY OF THE FORAMINIFERA. 179 



bered Foraminifera cast their shells at intervals to form 

 new ones — is, that they must occasionally be freed for 

 certain periods from the restraint of the shell, and be in a 

 condition to effect that spontaneous division which is so 

 striking a feature in the Ehizopoda. The specimens of 

 double shells which I have- observed, including six or eight 

 of Orbulina, four of Lagena, two of which are represented 

 on Plate IV. figs. 4, 5, and about half a dozen of different 

 varieties of Entosolenia, are all of them of medium size, 

 the pair in each case being together about equal to one 

 large specimen of the same species ; and these indicate, I 

 believe, that here the process of self-division was arrested 

 by the formation of the shell, probably to be again attempted 

 with better success after the next change of shell. I have 

 seen plenty of proof in Truncatulina lobata that fresh in- 

 dividuals may be formed by portions of the sarcode being 

 cast off from full-grown animals, and afterwards covered 

 by a shell ; for specimens are not at all uncommon con- 

 sisting either of a single chamber or of a group of two or 

 three chambers, perfectly agreeing in their general cha- 

 racter with the shell of Truncatulina ; but I have seen no 

 proof that this happens with the single-chambered forms, 

 though I have one curious specimen of a Lagena (Plate IV. 

 fig. 6) with a second very small one attached to its mouth, 

 which might at first sight be looked upon as a proof that 

 an off-shoot was here being detached, but before it could 

 get free had become fixed to the parent by a premature 

 formation of its shell. No specimens, however, anything 

 like so small as this, have been found loose in the sand, 

 which they ought to be if this were at all a usual mode of 

 increase ; and the interpretation of the specimen is, I be- 

 lieve, that the animal, instead of withdrawing itself from 

 its shell, either to form a new one of a larger size or to 

 divide, has taken the unusual course of adding a supple- 

 mentary chamber, just as in the instance before given of 



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