FORAMLNIFERA AND RADIOLARIA. 



75 



FIG. 317. 



originates from the ' circumambient segments;' for sometimes a score or 

 more of radial passages extend themselves from every part of the margin 

 of the latter (and this, as corresponding with the plan of growth after- 

 wards followed) is probably the typical arrangement) ; whilst in other 

 cases (as in the example before us) the number of these primary offsets is 

 extremely small. Each zone is seen to consist of an assemblage of ovate 

 sub-segments, whose height (which could not be shown in the figure) 

 corresponds with the thickness of 

 the disk ; these sub-segments, 

 which are all exactly similar and 

 equal to one another, are connec- 

 ted by annular stolons; and each 

 zone is connected with that on its 

 exterior by radial extensions of 

 those stolons passing-off between 

 the sub-segments. 



468. The radial extensions of 

 the outermost zone issue-forth as 

 pseudopodia from the marginal 

 pores, searcbing-for and drawing- 

 in alimentary materials in the 

 mannner formerly described ( 

 397); the whole of the soft body, 

 which has no communication 

 whatever with the exterior save 

 through these marginal pores, be- 

 ing nourished by the transmission 

 of the products of digestion from 

 zone to zone, through similar 



bands OI protoplasmic Substance, cumambient segment, giving off peduncles, in which 



In all cases in which the growth ^*ZSSSS?rt^ 

 of the disk takes place with nor- 

 mal regularity, it is probable that a complete circular zone is added 

 at once. Thus we find this simple type of organization giving origin 

 to fabrics of by no means microscopic dimensions, in which, how- 

 ever, there is no other differentiation of parts than that concerned in the 

 formation of the shell ; every segment and every stolon (with the exception 

 of the two forming the ( nucleus ') being, so far as can be ascertained, a 

 precise repetition of every other, and the segments of the nucleus differ- 

 ing from the rest in nothing else than their form. The equality of the 

 endowments of the segments is shown by the fact of which accident has 

 repeatedly furnished proof that a small portion of a disk, entirely sepa- 

 rated from the remainder, will not only continue to live, but will so in- 

 crease as to form a new disk (Fig. 318); the want of the ' nucleus' not 

 appearing to be of the slightest consequence, from the time that active 

 life is established in the outer zones. 



469. One of the most curious features in the history of this type is its 

 capacity for developing itself into a form which, whilst fundamentally 

 the same as that previously described, is very much more complex. 

 In all the larger specimens of OrbitoUte, we observe that the mar- 

 ginal pores, instead of constituting but a single row, form many rows 

 one above another, and besides this, the chamberlets of the two 

 surfaces, instead of being rounded or ovate in form, are usually oblong 

 and straight-sided, their long diameters lying in a radial direction, 



