ORBITOLITES 



809 



are interposed columnar chambers of a rounded form ; and these 

 last are connected together by a complex series of passages, the 

 nrrangement of which will be best understood from the examination 

 of a part of the sarcocle-body that occupies them (fig. 612). For the 

 oblong superficial chambers are occupied by sub-segments of sarcode, 

 c c, d d, lying side by side, so as to form part of an annulus, but 

 each of them disconnected from its neighbours, and communicating 

 only by a double footstalk with the two annular ' stolons,' a a! , b b r , 

 which obviously correspond with^he single stolon of ' simple ' types 

 (fig. 610). These indirectly connect together not merely all the 

 superficial chamberlets of each zone, but also the columnar sub- 

 segments of the intermediate layer ; for these columns (e e, e' e'} 

 terminate above and below in the annular stolons, sometimes passing 

 directly from one to the other, but sometimes going out of their 

 direct course to coalesce with 

 another column. The columns 

 of the successive zones (two sets 

 of which are shown in the 

 figure) communicate with each 

 other by threads of sarcode in 

 such a manner that (as in the 

 simple type) each column is 

 thus brought into connection 

 with two columns of the zone 

 next interior, to which it alter- 

 nates in position. Similar 

 threads, passing off from the 

 outermost zone through the 

 multiple ranges of marginal 

 pores, would doubtless act as 

 pseudopodia. 



Now this plan of growth is 

 so different from that previously 

 described that there would at 

 first seem ample ground for 

 separating the simple and the 

 complex types as distinct species. 

 But the test furnished by the 

 examination of a large number 

 of specimens, which ought never to be passed by when it can possibly 

 be appealed to, furnishes these very singular results : 1st, that the 

 two forms must be considered as specifically identical ; since there is 

 not only a gradational passage from one to the other, but they are 

 often combined in the same individual, the inner and first-formed 

 portion of a large disc frequently presenting the simple type, whilst 

 the outer and later-formed part has developed itself upon the complex ; 

 2nd, that although the last-mentioned circumstance would naturally 

 suggest that the change from the one plan to another may be simply 

 a feature of advancing age, yet this cannot be the case : since, 

 although the complex sometimes evolves itself even from the very 

 first (the ' nucleus,' though resembling that of the simple form, sending 



FIG. 612. Portion of animal of complex 

 type of Orbitolites complanata: 

 a a', b b', the upper and lower rings of 

 two concentric zones; c c, the upper 

 layer of superficial sub-segments, and 

 d d, the lower layer, connected with the 

 annular bands of both zones ; e e and 

 e' e', vertical sub-segments of the two 

 zones. 



