FORAMIXIFERA. 



[ 331 1 



FORAMINIFEEA. 



horizontal lines are seen (fig. 25 c) ; these 

 are the lines of C( intact of tlie hiyers com- 

 posing the shell, or the lines of growth. The 

 margin of the shell is traversed hy elongated 

 inosculating vessels, which cause the mar- 

 ginal portion to hreak up into calcar(>ou9 

 spicnla (iig. 24), 1-237" long and 1-900" 

 hroad. In a transverse section of the mar- 

 gin, more than 100 of these are seen, form- 

 ing a triangular bundle or cord (fig. 25 a), 

 the apex being directed towards the cham- 

 ber, the base outwards forming the free 

 rounded margin of the shell ; and parallel 

 to its side run the papillary tubes of the 

 chamber (tig. 25 b). 



In addition to the common foramina and 

 the oritices of the marginal plexus, the 

 chambers, especially those which terminate 

 the series, are furnishetl with other larger 

 orifices opening ext:ernally; these are of 

 various forms find ditlerently situated ; some- 

 times they are round, numerous, and 

 comparatively small; at others they are 

 single and large, circular, semicircular, or 

 lunate, &c. 



The nature of the Foraminifera has been 

 very difi'erently viewed. They were formerly 

 regarded as microscopic Cephalopoda, then 

 as Bryozoa (Polyzoa), and again as inter- 

 mediate between the Polypi and Echinoder- 

 mata. Dujaidin's view^, however, is now 

 fidopted, that their structure is very simple, 

 and that they are closely allied to the Arcel- 

 lina, the body being single and composed 

 of a simple sarcodic substance, without 

 the distinct separation of organs, the fili- 

 form processes (pseudopodia), which issue 

 from the various external apertures of the 

 shell being comparable with those of 

 Ainaha, Arcella, and other members of the 

 family. 



Tlie chambers contain a soft translucent 

 colourless substance ; and often one or more 

 minute, round, granular bodies (sarco- 

 blasts) are present. These appear to have 

 been sometimes regarded as nuclei. If the 

 corpuscles described by Hertwig and Schidze 

 as nuclei are really such, the Foraminifera 

 may be ranked as high as the Amoebina. 



The nature of the contents of the intra- 

 septal and marginal vessels is doubtful ; 

 Mr. Carter regards them as performing a 

 water-vessel function comparable to that 

 of the circulating system of the sponges 

 {Graiitia) ; whilst ^Villiamsonand Carpenter 

 consider them to be filled with the organic 

 substance (if the body. 



The shells of Foraminifera are rarely 



quite chitinous ; some have a chitinous base 

 with either a sandy or a calcareous coating. 

 Mostly they are altogetlu-r composed of 

 carbonate of lime, and therefore effervesce 

 with a dilute acid. By carefully acting 

 upon the recent organisms with muriatic 

 acid, in the proportion of a drop of the 

 strong acid to a watchglassful of water 

 containing them, the animal is left (PI. 23. 

 fig. 32), retaining the general foim of 

 the shell, which it has mouldi'd upon it- 

 self. 



In the ''porcellaneous" group the shell- 

 matter covers each segment of sarcode tent- 

 wise, the edges of the new" chambers resting 

 on the outside of the older part of the shell. 

 In the "hyaline" group each segment is,in 

 many cases, fully enwrapped with shell, 

 except at the septal orifice, through which 

 the stolon connects the new and old seg- 

 ments. Besides this tubuliferous shell-layer, 

 many of the hyaline Foraminifera lay down 

 other coats, by the investing sarcode, 

 before new segments are set off; and 

 these supplementary layers not only form 

 ridges and tubercles, but also the " inter- 

 mediate skeleton," in which vessels or 

 canals, for the sarcode passing outwards, 

 are more or less prevalent, constituting the 

 " Canal-system." 



Recent Foraminifera can be procured by 

 dredging, or sometimes from the sand of the 

 sea-shore. They often form white lines or 

 bands, between tide-marks. To separate 

 them, the sand should be washed in fresh 

 water, dried, and spread upon a piece of 

 black paper, or the black disk (Intbod, 

 p. xxvi), and examined as an opaque object ; 

 when the shells, easily distinguished by 

 their forms, may be picked out by means of 

 a mounted bristle. 



Or the dried sand may be stirred up with 

 water and allowed to settle ; the sandy par- 

 ticles will then subside, and the shells, from 

 their cliambers being filled with air, may be 

 skimmed off the surface ; or they may be 

 poured off through muslin, with the dis- 

 turbed water, before all the sediment has 

 had time to settle. 



In the fossil state, the Foraminifera 

 abound in Chalk, from which they may 

 be obtained in tJie manner directed under 

 Chalk ; in fact this substance constitutes 

 one of the best sources of them for exami- 

 nation. In other calcareous rocks or lime- 

 stones they are also extremely numerous. 

 Thus in the stones of which the buildings 

 in Paris are constructed, the shells of tlie 



