570 DR. W. B. CARPENTER ON ORBITOLTTES 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 devourers would 

 discriminate (for example) between the disks of a large 0. marginalis, a middle-sized 

 0. duplex, and a small 0. complanata, which 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 regiilar and uniform modes, who (in the 

 absence of the intervening links) would have suspected any genetic relation who 

 would 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 

 chamberletted 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 



