Mr. H. J. Carter on the Structure of the Foraminifera. 317 



while in other instances they are interrupted two or three times 

 by several turns of the cortical part alone (which part is analo- 

 gous to the spicular cord of Operculina), and that in the globose 

 Nummulites the chambers are frequently not distinguishable in 

 the outer turns, shows that the development of the test can go 

 on without the presence of the chambers, and therefore that they 

 are probably supplementary and propagative. Indeed, the ap- 

 proximation of the turns of the spire, or those of the spicular 

 cord, which, of course, must entail a corresponding diminution 

 in the size of the chambers, will be found by-and-by to indicate 

 the full size of the species, in which the subsidence of the genera- 

 tive force appears to be thus indicated. 



As yet, however, we know very little about the animal of 

 Foraminifera, chiefly because we are so ignorant of the forms 

 allied to it. The same is the case with the animal of SpongiUay 

 which I have described (Ann. Nat. Hist. vol. xx. 1857). It 

 fails to elicit much attention because, at present, it has no known 

 alliances ; but by-and-by, when these are found out and more 

 forms of the same kind are discovered for comparison, the 

 nature and position in organic development of these beings will 

 be realized and their component parts understood. Till then 

 they must remain in abeyance. 



Mode of growth. — The mode of growth in Operculina and 

 Nummulites is the same; that is, the horizontal portions, or 

 spiral laminfe as they have been termed by MM. d'Archiac and 

 Haime, are developed from the sarcode of the chambers passing 

 through the vertical tubuli, while the spicular cord and the 

 chambers in the first instance spring from the marginal plexus 

 of sarcodal filaments. The latter is shown in Alveolina, as above 

 stated, where the chambers cease to be developed and then ap- 

 pear again after several turns of the spire have been completed 

 by the cortical layer alone, which part, as before stated, is ana- 

 logous to the spicular cord. Both the segments of Operculina 

 and those of Nummulites begin to be formed from the spicular 

 cord, and three or more of the last are generally in successive 

 stages of development, the last of all being the least formed. 

 This must not, however, be confounded with the last chambers 

 of the fully-developed Operculina, which, like those of Nummu- 

 lites, arc also successiv-ely less in size. 



More recent Obseit-ations. — Since the above was written, I 

 have again determined, for examination, to sacrifice two or three 

 more of the few specimens I still possess of Operculina arabica 

 containing the living animal when they were brought up with 

 the "soimding-lead,^' on the south-east coast of Arabia, in 1844, 

 now of course dry ; and for this purpose one of these was placed 

 in very weak spirit and water for a night fii'st, another examined 



