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Transactions of the lioijal Micrcscojjical Society. 



than the others. Like as tLe few butterflies rising up to 

 the mountain top, have left the many floating in air among 

 the flowers in the valley, so these float upwards in the higher 

 regions of the water, whilst others remain below, — making their 

 tests of deep-sea sand or of spicula, or of Foraminifera themselves, — 

 or attached to rock, shell, or seaweed, — or lying free on the bottom, 

 with other organisms, to be preyed on by Dentaliuni (S. P. Wood- 

 ward) or Ophiura (at 1260 fathoms, Wallich), — to be used up in 

 the shells of some larger congeners, — to be accumulated in strata, 

 — or to be converted into such glauconite as coats the floor of the 

 Mexican Gulf with black-green sand. 



The difi'erences of depth at which these Microzoa live, and the 

 concomitant conditions of agitation or repose, of clear or muddy 

 water, much or little nourishment, of relative warmth and light, 

 are easily recognizable. Thus Pohjstomella has a thicker shell in 

 shallow than in deep water ; but Globigerina is thicker in deep than 

 in shallow ; and where it most abounds in abyssal waters, the 

 associated Foraminifera are often few in kind, few as individuals, 

 and very small. Possibly the greater amount of light and warmth 

 tliat the shallow-water Polystomellm and the floating GloMgerinse 

 enjoy, i'avours their growth beyond that of the more deeply seated 

 and the non-floating forms ; but others living even in deep water 

 have thick shells, either meeting with favourable conditions of 

 growth, or having grown thick before they sank to the bottom. 



The susceptibility of variation, by relative increase of size, or 

 by modification of shape and mode of growth, or by the thickening 

 and complexity of the shell, belongs to all the systematized groups 

 of Foraminifera. 



Systematic Grouping of Foraminifera. — There are said to be 

 4000 recognizably dilferent forms of these little Khizopodal shells, 

 such as a " superficial observer can separate by words and a name " 

 (Hooker), and these have been sorted according to their apparent 

 alliances into the several divisions of the appended Table (pages 

 89-92), copied by permission, with shght modifications, from 

 Henfrey and Grifiith's ' M icrographical Dictionary,' new edition, 8vo, 

 Van Voorst, London, ] 875. These groupings are based, primarily, 

 on the texture of the shell (whether " porcellanous," " hyaline," or 

 " sandy "), and secondarily on the arrangement of the segments of 

 sarcode, and the form of the shell-chambers. Neither the fixed 

 (parasitic) habit of shell, nor the single-chambered condition, has 

 weight in this classification, as neither is confined to any one group 

 of the Foraminifera. 



Arranged on this plan many dissimilar forms are found to be 

 mutual allies, and even more closely akin ; whilst, with some, an 

 external resemblance, .chiefly from mode of growth, is mimetic 

 only, — or, rather, a real bond of relationship, arising from the 



