206 DR. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



of note, that whatever differences of this -kind may exist, they are entirely due to the 

 variable length of the columns of the intermediate stratum ; the depth of the cells 

 of the superficial layers being- nearly constant, and no vertical multiplication of these 

 ever taking place. The intermediate stratum, where it abuts on the nucleus, is often 

 very thin ; the annular stolons that run beneath the superficial layers being in such 

 near proximity to each other, that the intervening column of sarcode is very short, 

 and consists of only a single vertical segment, Plate V. fig. 12. 



33. The foregoing description applies in every particular to those specimens only, 

 which present the structure of this type of Orbitolite in its most regular and charac- 

 teristic development ; and the differences between this more complex form, and the 

 simple form previously described, are such as at first sight to preclude the idea of 

 their specific identity. Hence I am not in the least degree surprised, that Professor 

 WILLIAMSON, by whom their respective plans of organization were first compared 

 (loc. cit.), should have unhesitatingly regarded these two forms as specifically distinct. 

 But when a large number of specimens of the more complex type are carefully 

 examined and compared with each other, it becomes obvious that a vast amount of 

 diversity in the arrangement of the cells of the shell, and of the segments of the 

 animal, may present itself; and that one after another of the characters which at first 

 seem most clearly marked and therefore most distinctive, may be shaded off (so to 

 speak) in such a manner that a complete transition is established, sometimes even in a 

 single disk, between the simple and complex types. Such a transition is exhibited 

 by the specimen of which a vertical section is figured in Plate V. fig. 7; for it is 

 obvious that the central portion of this disk (a b) is so exactly conformable to the 

 simpler type, that if this growth had stopped at the twenty-third zone, it would have 

 undoubtedly been regarded as an unusually large example of that form. So many 

 variations present themselves in the development of the different parts of the more 

 complex type, that it will be desirable to describe them under a distinct head 

 (Sect. IV.) ; and when these shall have been duly considered, I think that all doubt 

 as to the specific identity of the simpler and more complex forms will be done away. 



III. Physiology. 



34. Growth. Of the mode in which the Nutritive process is carried on in Orbito- 

 lites, our imperfect acquaintance with their living habits leaves us much in the dark ; 

 nevertheless it is fair to reason by analogy from a comparison of their structure with 

 that of other Foraminif'era whose habits of life are known ; especially as this analogy 

 is sufficiently complete in the present instance, to justify a tolerably firm reliance 

 upon it, and as the results to which it would lead are in harmony with the facts of 

 observation. All the Orbitolites, whether of the simple or complex type, which have 

 been collected in the living state, have been found growing on the surface of Sea- 

 weeds or other marine plants (as Zostera), or of Zoophytes ; it may therefore be fairly 

 presumed, that such is their ordinary habitat ; and hence it is scarcely conceivable 



