DE. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 567 



body of 0. tenuissima; on the other hand, I have not met in the higher types with 

 those nuclear (?) bodies which I have recognised in the abyssal species (see p. 556). 



The homogeneousness of the entire sarcodic body, even in the largest and most com- 

 plicated forms of O. complanata, appears to be further indicated by the fact, that in 

 specimens taken alive and preserved in spirit, the peripheral portion of the cavitary 

 system is invariably found empty ; the sarcodic body, corrugated by the action of the 

 spirit, being drawn together towards the central portion of the disk through very 

 narrow passages of communication, which could only happen with a substance of which 

 every part is free to move upon every other. Looking, also, to the manner in which 

 the entire organism receives its nourishment through the marginal pores, and to the 

 entire absence of any special means for the distribution of that nourishment, I think 

 it may be fairly assumed that such a protoplasmic circulation goes on throughout life, 

 as must produce a continual change in the substance of every individual sub-segment. 



Additional evidence of this homogeneousness is afforded by the two following facts : 

 first, that in specimens which live under conditions peculiarly favourable to their 

 enlargement, out-growths of irregular shape, but always possessing a regular internal 

 structure, are put forth from any part of the disk (see " Challenger " Report, Plate 

 VII.) ; and second, that, as in 0. tenuissima, every part seems equally capable of 

 reproducing the entire disk on its characteristic plan. 



Evolutionary History of the Orbitoline Type. 



Thus by the combined study of O. tenuissima and of sub-typical examples of 

 0. complanata, we are enabled to work out the whole evolutionary history of the Orbi- 

 toline type, from its simplest to its most complex form. For there can, I think, be no 

 reasonable doubt, that the succession here presented to us in the consecutive phases of 

 two lives, has been the genetic history of this type ; w T hich, originating in the simplest 

 "jelly-speck " that could form a shelly chamber, first assumed the form of a spirally- 

 coiled undivided tube (Cornuspira, fig. VII., 1) ; then of a spire interrupted at inter- 

 vals by imperfect partitions (Spiroloculina , 2) ; then of a flattened spire crossed by 

 complete septa traversed by stolon-passages (Peneroplis, 3) ; then of a progressively 

 widening spire, whose chambers are divided into chamberlets (Orbiculina, 4) ; then of a 

 chamberletted disk of one storey, commencing as an orbiculine spire, but subsequently 

 increasing by annular additions (Orbitolites tenuissima and 0. marginalis, 5) ; then of 

 a chamberletted disk, whose origin still shows in its slight eccentricity a trace of the 

 primordial spire, and whose single storey has, so to speak, two rows of windows 

 (Orbitolites duplex, 6) ; and lastly, of a " complex " disk, whose growth is cyclical 

 from the beginning, and whose upper and lower superficial planes are separated by 

 the interposition of an intermediate columnar structure between the duplicated 

 annular stolons (Orbitolites complanata, 7). This last would seem to be the culmina- 

 tion of the type, which, while attaining a considerable size, has never shown, so far 



4 D 2 



