FORAMINIFERA. i ' '*'/ ' J * IQ1 



wall of shell. In these " multilocular " or " polythalammis;" 

 Foraminifera, therefore, the shell ultimately comes to consist 

 of a series of chambers, separated by partitions of the test, 

 and filled with sarcode. The partitions, however, or "septa," 

 between the different chambers, are perforated by one or 

 more apertures, through which pass connecting bands, or 

 " stolons," of sarcode ; so that the sarcode occupying the 

 different chambers is united into a continuous and organic 

 whole. Each segment may give out its own pseudopodia 

 through perforations in its investing wall (fig. 13, c), or the 

 pseudopodia may be simply emitted from the mouth of the 

 shell by the last segment only (fig. 13, &). In any case the 

 direction in which the segments are developed is governed 

 by a determinate law, and differs in different species, the 

 form ultimately assumed by the shell depending wholly upon 

 this. The forms, however, assumed by the shells of Fora- 

 minifera are extremely variable, even within the limits of a 

 single species, and it would be impossible to notice even the 

 chief types in this place. There are, however, two or three 

 important variations which may be noticed. If the buds are 

 thrown out from the primitive spherule in a linear series so 

 as to form a shell composed of numerous chambers arranged 

 in a straight line, we get such a type as Nbdosaria (fig. 13, 

 e). When the new chambers are added in a spiral direction, 

 each being a little larger 

 than the one which pre- 

 ceded it, and the coils of 

 the spiral lying in the same 

 plane, we get such a form 

 as Discorbina (fig. 13, c), or 

 Robulina (fig. 15). These 

 are the so-called "nautiloid" 

 Foraminifera, from the re- Fi - ^--cnsteiiarm (tobuiina) echiwta, a 



J . " nautiloid " Foraminifer. (D'Orbigny.) 



semblance of the shell, in 



figure, to that of the Pearly Nautilus. From this resem- 

 blance the nautiloid Foraminifera were originally placed in 

 the same class as the Ammonites (Cephalopoda), but their 

 true position was shown by the examination of their soft 

 parts. In the typical nautiloid shell the convolutions 



