GENUS MILIOLA. 



77 



Diagvaiiiiuulic ie(jrcscii- 

 tation of tlie Animal of 



Hence it is ob- 



106. The conformation of the sarcode-body of the animal obtained by the decalcification 

 of the shell, exactly corresponds with what the characters presented by its envelope would 

 lead us to anticipate. Starting from the ordinary primordial segment 



(Fig. XIV, o), we find this giving origin, by a constricted neck or lu;. XR. 



"stolon," to the first longitudinal segment 1, which doubles round one 

 side of it, and is then again constricted into a " stolon ;" from this pro- 

 ceeds the second longitudinal segment l', whicli passes round the other 

 side of the primordial spheroid, and, liaving extended itself beyond the 

 first, narrows itself at the opposite end of the diameter into a stolon ; from 

 this proceeds a third longitudinal segment 3, whicli passes round the 

 first and extends beyond it, giving origin, by a constricted stolon, to a 

 fourth 1, which in like manner passes round the second and extends 

 beyond it ; and this mode of increase may continue until a considerable 

 number of segments have lieen formed on either side of the primordial 

 spheroid, the last extending itself into pseudopodia at its termination, 

 vious that each segment grows in a direction contrary to that of the segment which 

 immediately preceded it, but corresponding to that of the ante-penultimate ^segment; 

 and that the pseudopodial extensions will be put forth alternately from one and the other 

 extremity of the body. And it is further obvious that this Milioline type involves, so 

 far as the structure of the animal is concerned, no more considerable departure from the 

 simple type of Coriui^piva than that which is produced by the narrowing of the spire as it 

 crosses each end of its long diameter, — a conclusion which derives additional support from 

 tlie exact conformity to the Coniuxpiru type, whicli, as already shown (^ 49), is presented bv 

 the young oi j\liIioIa (see xcvtt, plate ii, figs. 1 — 6). 



107. The cliaractcrs adopted by D'Orbignv for the differentiation of his genera are for 

 the most part furnished by the number of chambers which show themselves externallv : a 

 variation whicli depends upon the degree in which the later chambers invest the earher, upon 

 the symmetry of their shape, and upon the mode in which they arc disposed with reference 

 to the diameter of tlie spire. Thus if the successive segments simply increase in diameter 

 without departing much from their primitive cylindrical 

 form, so that the successive chambers of the shell merely 

 apply themselves to the external surfaces of those which 

 preceded them, then the whole series of chambers is visible 

 on each side of the adult slicll ; and the ^fJIUdu which 

 grows upon this plan, wliicli will be readily understood 

 from the ideal transverse sections shown in Fig. XV, 

 is distinguished as Spiroloculina (Plate VI, figs. 1, 2). If, 

 however, the segments of sarcode extend themselves on 

 either side into " alar lobes," and these are symmetrically 

 prolonged so as completely to cover each side of the cham- 

 bers to which they are applied, as shown in Fig. XVI, 

 then only in-o chambers — the last and the penultimate — 

 are visible externally, and we have a Wdoadma (Plato VI. fig. 7).' It often happeu- 



FiG. X\ 



Idi'al transverse sections of Spli'ijloadl-uf. 



