452 NATURE AND MAN. 



culina, coiling continuously round a primordial chamber, as in 

 Cornuspira. Thus, in this interesting organism \ve find permanently 

 represented the whole developmental history of the &quot; simple &quot; type 

 of Orbitolite from the primordial jelly-speck. The large Challenger 

 collection of Orbitolites, made on the Fiji reef, has furnished me 

 with the means of still more completely working out the transition 

 from the simple&quot; to the &quot;complex&quot; type; a distinctly inter 

 mediate type there presenting itself in great abundance. This, 

 which I term the &quot;duplex&quot; type (Fig. VI., i), resembles the 

 &quot;simple&quot; in having its annular series of chamberlets disposed in 

 a single plane, and in the connection of the chamberlets of each 

 ring by a single annular canal ; but differs in having its successive 

 rings connected by a double series of radial passages, which issue 

 on the edge of the disk (Fig. VI., 2) as marginal pores. The 

 columnar sub-segments, a a , b b , of each ring are strung, as it 

 were, on the annular cord, c c 1 ; and this sends off an upper and 

 a lower series of stolon-processes, d d, d d , which pass into the 

 upper and lower halves of the sub-segments of the next ring. 

 The plan of growth in the first-formed portion, shown in Fig. VI., 

 3, is singularly intermediate between that of the &quot;simple &quot; and that 

 of the &quot; complex &quot; type. The regular spire of the former is now 

 reduced to the single turn made by the &quot;circumambient segment,&quot; 

 b b, round the &quot; primordial segment &quot; a ; but a partial continuance 

 of the same plan is shown in the incompleteness of the first two or 

 three rings of sub-segments ; these being budded forth from only 

 half of the &quot; circumambient segment,&quot; instead of from its whole 

 periphery, as in the typical &quot;complex&quot; Orbitolite. (Fig. II.). Yet 

 even in large disks, whose later growth is characteristically &quot;com 

 plex,&quot; the nucleus and earlier rings are often formed on the 

 &quot;duplex&quot; plan, which passes into the &quot;complex&quot; in the manner 

 to be now described. 



Believing, with Sir James Pagct, that &quot; the highest laws of 

 &quot;biological science are expressed in their simplest terms in the 

 &quot; lives of the lowest orders of creation,&quot; I shall now ask you to 

 follow me through a detailed examination of the transition from 

 one type to the other; as shown in Fig. VII., which represents 

 a vertical section, taken in a radial direction, of one of those large 

 &quot;complex&quot; disks whose life was commenced on the plan of the 



