1849.] CARPENTER ON THE STRUCTURE OF NUMMULINA. 29 



the deposition of new matter upon that portion of the central nucleus 

 which is not covered by the investing whorls ; and in this view he is 

 in accordance with M. D'Orbigny, who, in his recent work ' Surles 

 Foraminiferes Fossiles du Bassin Tertiaire de Vienne,' fully recog- 

 nizes the power of the pseudopodia to secrete the calcareous cover- 

 ing. I may remark, that I cannot see how the investing layers 

 covering the disk of Nummulites complanata, and the other species 

 of the same group, can be formed in any other way ; since, in these, 

 the chambers are only marginal, the segments of the animal not ex- 

 tending over the disk ; and we have no reason to believe in the 

 existence of any external mantle, spreading over the whole surface, 

 whereby these investing layers could be formed. 



It is worthy of remark, that, in the outer whorls, the two laminae 

 of the septa diverge from each other, as in Nummulites, where they join 

 the outer margin of the chamber ; and that they thus leave an inter- 

 septal space, towards which certain prolongations of the animal struc- 

 ture appear to pass. If it should be found that the pseudopodia 

 arise from these, the resemblance of the animal of Folystomella crispa 

 to that by which the shell of Nummulite was probably formed, would 

 seem to be very close. 



The view which we take of the individuality of the segments of 

 the animal of Nummulite, must depend upon the ideas we entertain 

 regarding the nature of similar aggregations in other Foraminifera, as 

 well as in Zoophytes and the inferior Mollusca. The several segments 

 appear to be, in all essential particulars, mere repetitions of each 

 other ; they are formed by successive gemmation from a single pri- 

 mordial segment ; and when this gemmation has taken place, the 

 newly-formed segment appears to be as independent of the rest, as 

 are the several polypes in a polypidom. There is no indication that 

 the inner and earlier segments derive their nourishment through 

 their connection with the outer and last-formed ; on the contrary, 

 there is every indication that the former continue to maintain the 

 same communication with the exterior which they ever had; and 

 that the necks which are prolonged through the apertures in the 

 septa are rather to be considered in the light of stolons or creeping 

 stems, from which new gemmae are to be produced, than as re- 

 sembling an intestinal canal common to the whole series of segments. 

 We may consider the entire structure, then, either in the light of a 

 series of distinct individuals developed by gemmation from the first- 

 formed segment, like the clusters of the compound Tunicata ; or as 

 a single aggregate being, made up of an assemblage of similar parts 

 indefinitely repeated. It does not seem to me of much consequence 

 to decide between these two views, if we distinctly recognize the 

 essential independence of the segments, and their multiplication by 

 gemmation. This is a matter of some importance in regard to the 

 determination of species ; for if we are to consider Nummulites as 

 analogous rather to the polypidoms of Zoophytes or Bryozoa, than 

 to the shells of the Mollusca, it is obvious that we must allow for a 

 considerable amount of variation in their form, vdthout any trans- 

 gression of specific limits. It is well known that many species and 



