I 



I 



British species of the genus Lageiia. 7 



The above opinions are at variance with those of M. Ehrenberg, 

 who considers that the calcareous case of the Foraniinifer is 

 merely the dried skin of the animal, containing dendritic calca- 

 reous particles, which on the contraction of the skin closes and 

 conceals orifices through which the food is received. His ob- 

 servations which led to the above conclusions were chiefly made 

 upon the curious little Sor-ites orbiculus, Ehr., the Nummulina 

 nitida of D'Orbigny. However much this organism may support 

 his opinion, certainly the Rotalina Beccarii and similar genera 

 do not. We have no evidence that the external parietal fora- 

 mina have an extensile and contractile property ; and even if the 

 large orifices of Rosalina globularis had any such power, we have 

 demonstrative proof that the orifices do not penetrate the lining 

 membrane, into the interior of which the food would have to find 

 its way. M. Ehrenberg rests his argument upon the discovery 

 of small siliceous organisms in the interior of the cells. It is 

 possible that the oraP. orifice may be capable of some degree of 

 extension, allowing the transmission of objects of this kind. In 

 Membranipora, Eschar a and other allied groups, the analogous 

 parietal foramina are obviously employed for no such purpose 

 as the transmission of food, which is received through the large 

 orifice at the extremity of the cell. Though the fact that these 

 latter objects are furnished with true polypes may make a dif- 

 ference, still is it not probable that there may be a resemblance 

 in the functions of such closely corresponding foramina in objects 

 so nearly allied ? At the same time I may observe, that I have 

 never found siliceous organisms of any size in the smaller inter- 

 nal chambers of Rosalina, Rotalime, &c., though the frustules of 

 Cocconeis, Grammatophora and Navicula are not uncommon in 

 the larger cells, where the communicating apertures are propor- 

 tionately large. 



One of M. Ehrenberg's results is much more analogous in some 

 respects to those obtained by Milue Edwards, in his investiga- 

 tions into the structure of Eschara. The latter observer has clearly 

 shown that the cells of this animal are thickened by external ad- 

 ditions of calcareous matter, and that, consequently, the soft 

 animal membrane does not line the internal cavity, but pervades 

 the whole substance of the calcareous cell ; the calcareous atoms 

 not being developed upon, but in the skin of the animal. From 

 this it is evident, that very dilferent modes of growth and deve- 

 lopment are to be found in animals otherwise closely allied. 



I have found that M. Ehrcnbcrg^s remarks on the soft animals 

 of the Foraminifera apply strikingly to that of Rosalina ylobu- 

 laris, but scarcely to any other of those that I have examined. 

 In this species, the animal membrane, lining the smaller cells of 

 what in a shell would be called the spire, is of a rich brown co- 



