COMPLEX TYPE OF OEBITOLITES. 49? 



each of them being disconnected from its neighbours, and commu- 

 nicating only by a double footstalk with the two Annular Stolons, 

 a a\ b b\ which obviously correspond with the single stolon of the 

 Simple type (Fig. 251). These indirectly connect together not 

 merely all the superficial Chamber lets 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 the 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 alternates in position. Similar 

 threads, passing off from the outermost zone, through the mul- 

 tiple ranges of Marginal Pores, would doubtless act as Pseudo- 

 podia. ^Now this plan of growth is so different from that pre- 

 viously 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 iden- 

 tical ; 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 Disk frequently pre- 

 senting 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 the Complex 

 sometimes evolves itself even from the very first (the Nucleus, 

 though resembling that of the simple form, sending out two or 

 more tiers of radiating threads), whilst, more frequently, the 

 Simple prevails for an indefinite number of Zones, and then 

 changes itself in the course of a few zones into the Complex. A 

 more striking instance could scarcely be drawn from any depart- 

 ment of Natural History, of the wide Range of Variation that 

 may occur within the limits of one and the same Species ; and 

 the Microscopist needs to be specially put on his guard as to this 

 point, in respect to the lower types of Animal as to those of 

 Vegetable life, since the determination of form seems to be far less 

 precise among such, than it is in the higher types.* 



• For a fuller account of the Organization of Orbitolites, and of the 

 various conditions under which it presents itself, see the Author's Memoir 

 upon that Genus in the "Philosophical Transactions," 1856, and his 

 " Introduction to the Study of the Foraminifera," published by the Ray 

 Society, 1862. 



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