570 
DR. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 
tionary history of the typical Orbitolites, from Cornuspira to Spiroloculina, from 
Spiroloculina to Peneroplis, from Peneroplis to Orbiculina, from Orbiculina to the 
“ simple ” forms of Orbitolites, and from the “ simple ” to the “ complex ” forms of the 
last-named type. And as all these earlier forms still flourish under conditions which 
(so far as can be ascertained) are precisely the same, there is no ground to believe 
that any one of them is better fitted to survive than another. They all imbibe their 
nourishment in the same mode ; and no one type has more power of going in search 
of it than another. That they are all dependent on essentially the same conditions of 
temperature and depth of water, is shown by their occurrence in the same marine 
areas. That they all equally serve as food to larger Marine Animals, can scarcely 
be doubted; and it is hardly conceivable that any of their clevourers would 
discriminate (for example) between the disks of a large 0 . marginalis, a middle-sized 
0. duplex, and a small 0. complanata, wdiicli even the trained eye of the Naturalist 
cannot distinguish without the assistance of a magnifying-glass. 
To me, therefore, it appears that the doctrine of “ natural selection ” can give no 
account of either the origin or the perpetuation of those several types of Foraminiferal 
structure which form the ascending series that culminates in Orbitolites complanata. 
On the other hand, there seems traceable throughout that series a plan so definite 
and obvious, as to exclude the notion of “ casual ” or “ aimless ” variation. Between 
the simple spirally-coiled sarcodic cord of a young Cornuspira, and the discoidal body 
of an Orbitolite, with its thousands of sub-segments disposed with the most perfect 
symmetry, and connected together in most regular and uniform modes, who (in the 
absence of the intervening links) would have suspected any genetic relation—who 
w r ould have ventured to construct a pedigree ? And yet we find the gradations from 
the one to the other to be not only most complete, but often significant of further 
progress ; many of the changes being such as seem to have no meaning except as 
anticipations of greater changes to come. Thus, the slight constrictions that show 
themselves in the first spiral coil of 0. tenuissima (Plate 38, fig. 3) are what constitute 
the essential difference between the spire of Cornuspira and that of Spiroloculina; 
marking an imperfect septal division of the spire into chambers, which cannot be 
conceived to affect in any way the physiological condition of the contained animal, but 
which foreshadows the complete septal division that marks the assumption of the 
Peneropline stage. Again, the incipient widening-out of the body, previously to the 
formation of the first complete septum, prepares the way for that great lateral exten¬ 
sion which characterises the next or Orbiculine stage; this extension being obviously 
related, on the one hand, to the division of the chamber-segments of the body into 
cliamberletted sub-segments, and, on the other, to the extension of the zonal chambers 
round the “ nucleus,” so as to complete them into annuli, from which all subsequent 
increase shall take place on the cyclical plan. 
In 0. marginalis, the first spiral stage is abbreviated by the drawing-together 
