456 NATURE AND MAN. 



by looking at the progressive complication in the structure of the 

 sarcodic body on which the shell is modelled. First, we have a 

 simple pear-shaped particle, extending itself into a cord that lies 

 in a continuous spiral around it, with constrictions at intervals. 

 This spire flattens out ; and then, by the formation of transverse 

 partitions, traversed by pores, the successive additions become 

 segmentally separated from each other, though mutually connected 

 by sarcodic extensions. Next, these segments undergo a further 

 division into sub-segments : all those forming each row being 

 strung (as it were) on a continuous sarcodic cord, which connects 

 them laterally ; while the successive rows are connected, as before, 

 by radial &quot; stolon processes,&quot; those of the last-formed row issuing 

 forth through the marginal pores, as the pseudopodia, through 

 which nutriment is absorbed for the entire body. Then, by the 

 opening out of the spire, the lateral connecting cords become 

 complete rings, from which the radial stolon-processes are given 

 off; and the future increase of the &quot;simple &quot; type consists in the 

 formation of new circular series of sub-segments, each strung, as 

 it were, on its own annular cord. Now, the advance towards the 

 &quot; complex &quot; type is prepared for, so to speak, by the sending forth 

 of two sets of radial stolon-processes instead of one ; a change 

 which, taken by itself, is meaningless, since every one who is 

 familiar with the variability of the Rhi/.opodal type (especially as 

 exhibited in the transitional forms between Peneroplis and Den- 

 dritind) knows that it cannot make any difference to the animal 

 whether its pseudopodia issue from the margin of the disk, through 

 a single or through a double row of pores ; but which is full of 

 meaning when regarded as a preparation for that splitting of each 

 annular cord into two, in which the transition from the &quot; simple &quot; 

 to the &quot; complex &quot; type essentially consists. Every annulus of 

 the body of the latter consists of a series of columnar segments 

 (Fig. VIII., e e, e &amp;lt;? ), passing at each end into an annular cord 

 (a a , b b }, and communicating with the series internal and 

 external to it, by oblique stolon-passages, the number of which is 

 related to the length of the columns ; this again, determining the 

 thickness of the calcareous disk which is modelled upon them. 

 The sub-segments of the two superficial layers (c c, d d) do not 

 communicate with each other ; but those of each circlet are con- 



