566 DE. W. B. CARPENTER ON ORBITOLITES TENUISSlMA. 



cut off from any other communication with them than that which is afforded by the 

 annular canals, with which each superficial chamberlet communicates at either end, 

 by a passage which thus traced out is seen to be homologous with one of the double 

 radial stolon-passages of 0. duplex, and therefore with the single radial passage of 

 O. marginalis. The septa, i i, which divide the median portions, m m, of the 

 successive annuli, are traversed by numerous passages, which, from the lateral 

 obliquity of their direction (fig. III., B,f,f), scarcely show themselves in a radial sec- 

 tion, although they debouch at the edge of the last annulus as marginal pores, mp. 



Notwithstanding this progressive complication in the structure of the shelly disks, 

 there is no appearance of any corresponding specialisation in the character of the 

 sarcode body: that of the typically " complex " form showing no other advance upon the 

 very simplest, than is marked by the duplication of the sarcodic annuli, by the separa- 

 tion of the superficial from the intermediate columnar sub-segments, and by the multi- 

 plication of the oblique stolon-processes which connect these last with each other, this 

 multiplication being obviously in relation with the increasing length of the interposed 

 columns, which shows itself in the thickening of the disk. The most marked increase 

 in the complication of the animal body obviously consists in the duplication of the 

 sarcodic annuli ; and this may be readily conceived as a longitudinal splitting of each 

 cord into two, with a persistence of adhesion at intervals, so that the two semi-annuli, 

 when carried apart from one another by the interposition of the intermediate stratum, 

 remain connected by the vertical sarcodic columns which traverse that stratum. The 

 sub-segments which occupy the upper and under layers of surface -chamberlets are 

 clearly shown, by their relation to the sarcodic annuli, not to be new productions, but 

 to be homologous with the upper and under halves of the sub-segments that occupy 

 the columnar chamberlets of the " simple " type ; that homology, however, being so 

 masked in the typically " complex " form by the displacement they have undergone, 

 that it could not have been certainly recognised, but for the occurrence of those sub- 

 typical forms which enable the passage from the most "simple" to the most "com- 

 plex " to be contimiously traced-out. 



I have been unable, after the most careful examination of the sarcodic bodies of 

 0. duplex and 0. complanata, to discover any indication that this progressive complica- 

 tion in the disposition of their parts, is accompanied by any such structural modification 

 as might lead to the suspicion of differentiation of function. On the contrary, I find 

 their substance to be everywhere of the same elementary character, consisting of a 

 homogeneous protoplasm, that contains a large number of spherules of from 6"^ooth to 

 aoouih of an inch in diameter, sometimes crowded closely together, in other instances 

 more dispersed, as shown in fig. 3, Plate IV. of my former Memoir (Phil. Trans., 

 1856). These spherules, when subjected to pressure, break up into a number of 

 pellucid corpuscles, which are usually of from 7-5 ^ro^th to aooooth of an inch in diameter. 

 The absence of these spherules is a marked feature of difference in the protoplasmic 



