66 Transactions of the Boijal Microscojjical Society. 



If the perforated Botalinee figured by Ehrenberg and Joseph 

 Wri'^ht should prove to be siliceous (as indeed the Antrim speci- 

 men is, though possibly from pseudomorphic change), we have 

 already noticed analogous intermediate examples * Ehrenberg's 

 original Spirillina vivipara is described as being siliceous ; and is 

 a perfect analogue of our common Spirillinfe,. Possibly some of 

 the common small Microzoa, passing for Foraminifera, under the 

 microscope, with transmitted hght, are really siliceous, and require 

 careful examination with the polariscope. 



" I should rather infer," wrote Professor W. C. Williamson, in 

 1858, " that the hard shells of the Foraminifera do not constitute a 

 sufficiently constant and important element in their organization 

 to justify our trusting to them as guides in the discrimination of 

 species ; " and others since then have fully agreed with him, almost, 

 if not quite, to the extent of regarding not only the Forami- 

 nifera, but even " the entire group of the Khizopoda," incapable of 

 specific division.! Still the shells have their zoological meaning ; 

 for, being variously formed by the sarcode, they refer to some 

 processes of Hfe and some habits of body, some peculiarities of 

 individuals and races, which in higher and more complex animals 

 give specific characters,^ but here, unaccompanied by other fixed 

 features of superadded parts, lose their distinctiveness among imi- 

 tative repetitions, and are thus lost in changes due to the general 

 adaptability of the sarcodic creature to the varied conditions of its 

 watery life. Certain as it is that the shells cannot supply grounds 

 for specific distinction, yet their texture and form have the impress 

 of the vital actions of an organism of which frequently httle else is 

 tangible ; and hence they are important elements in grouping the 

 Foraminifera. It is difficult to appreciate the physiological value 

 of such apparent or presumed organization as is met with in the 

 soft parts of these Protozoa, alive or dead, under the microscope, 

 even when well seen ; it is difficult to adjudge the relative value 

 of the several methods of producing and using the pseudopodial or 

 other extensions of sarcode ; their modes of existence, their indi- 

 vidual development and growth, are very imperfectly known. The 

 differences in function and habit and mode of growth may be quite 

 fixed in the several groups of individuals, or not : if fixed, they 

 give specific characters ; if interchangeable, whether by stages, by 



* See ' Proc. Belfast Nat. Hist. Field Chib,' ser. 2, vol. i., pp. 87, 88. 



t Williamson, ' Eecent Brit. Foram.,' p. x. 



J Professor W. C. Williamson says, " Such differences in the chemical and 

 histological composition of these sliells probably indicate correlate physiological 

 diiierences in the living sarcode, or secreting animal substance, the.t have at least 

 a specific value" ('Kecent Brit. Foram.,' p. xii.). The same form of shell (as 

 in ConiHspira, Trochammind, and Spirillinn, for instance) being represented in the 

 three groups (Imperforate, Arenaceous, and I'erforate), should not invalidate 

 the grounds for specific distinction unless the structural difl'ereuccs fail to hold 

 good. 



