FORAMINIFERA. 



[ 270 ] 



FORAMINIFERA. 



viewed. The Foraminifera were formerly con- 

 sidered as microscopic Cephalopods. Ehren- 

 berg regards them as belonging to the Bry- 

 ozoa among Polypes; viewing the several 

 chambers as either inhabited in common by 

 a single individual after the manner of the 

 Mollusca, or each chamber by a distinct 

 animal, as in Flustra, &c. ; and the siphonal 

 apertiu-es as corresponding to so many distinct 

 individuals in each chamber. This author 

 also states that the first and largest cell, some- 

 times also the second, and occasionally those 

 as far back as the fourth, frequently contain 

 the transparent part of the animal only; 

 whilst beyond this, the cells are filled with 

 two difi^erently-coloured organs ; one and 

 the principal, gray or greenish, representing 

 the alimentary canal and frequently contain- 

 ing Diatomaceae ; the other being yellowish 

 and forming the ovarium ; some of the 

 smaller cells being empty. 



On the other hand, Dujardin, with whom, on 

 the whole, later authors agree, views the Fora- 

 minifera as allied to the Arcellina ; regarding 

 the body as single, and composed of a simple 

 sarcodic substance, without the distinct sepa- 

 ration of organs ; and the filiform processes 

 (pseudopodia) which issue from the various 

 external apertures of the shell, as comparable 

 to those of Amceba, Arcella and other mem- 

 bers of the family. Certain it is, at least, 

 that delicate filiform processes issue from the 

 common foramina in the shell (PI. 18. fig. 19), 

 by the aid of which locomotion and perhaps 

 nutrition are performed. The same functions 

 are probably to be attributed to the tentacle- 

 like processes which are protrusile through 

 the larger orifices (fig. 18a). The nature of 

 the contents of the intraseptal and marginal 

 vessels is doubtful ; Mr. Carter regards them 

 as performing a water-vessel function com- 

 parable to that of the circulating system of 

 the sponges ( Grantia) ; whilst Mr. William- 

 son considers them to be filled with the 

 organic substance of the body. 



There is an evident analogy between the 

 structure of the shell in the Foraminifera, 

 and that of some Cephalopoda {Nautilus) ; 

 in the general form, the occurrence of the 

 septa and of the sipho. But there is a curious 

 difference between the arrangement of these 

 parts in the two instances ; for in the Fora- 

 minifera the septa are convex outwards or 

 towards the last chamber, towards which also 

 the sipho is prolonged, whilst in the Cepha- 

 lopods those relations are inverted. 



The shells of the Foraminifera are com- 

 posed principallj' of carbonate of lime, and 



therefore effervesce copiously when a dilute 

 acid is added to them. By carefidly acting 

 upon the recent organisms with muriatic 

 acid, in the proportion of a drop of the strong 

 acid to a watch-glass full of water containing 

 them, the animal is left (PI. 18. figs. 5, 8, 

 20), retaining the general form of the shell, 

 which it has moulded upon itself. 



Recent Foraminifera can be procured by 

 dredging, or sometimes fi'om the sand of the 

 sea-shore. In the latter case, the sand 

 should be spread upon a piece of black paper, 

 or the black disc (Introd. p. xxiii), and 

 examined as an opake object; when the shells 

 may be easily distinguished by their forms 

 and separated. 



In the fossil state, the Foraminifera abound 

 in chalk; from which they may be obtained 

 in the manner directed under Chalk ; in 

 fact, this substance constitutes the best 

 source of them for examination. In certain 

 calcareous rocks or limestones, they are also 

 extremely numerous. Thus, in the stone of 

 which the buildings in Paris are constructed, 

 the shells of Miliola, Lam., are so abundant, 

 that this city may be said to be built of 

 them. 



The shells of the nummulites or coin- 

 stones which form mountains in the Medi- 

 terranean regions, and of which the pj^amids 

 of Egypt are principally composed, agree in 

 essential structm-e with those of the Forami- 

 nifera (PI. 18. fig. 29). 



The following arrangement of a few of the 

 most common or interesting forms of the 

 Foraminifera may serve as an index to the 

 genera and species selected for illustration ; 

 but it is far from certain that the interpreta- 

 tion given to the structural appearances is 

 correct. 



Monosomatia. A single animal in each cell. 



Fam. 1. MiLiOLiNA. Shell simple, body not 



jointed. Two genera: Miliola, Ehr. (not 



Lam.), in which the shell is calcareous; 



and Gromia, in which it is membranous. 



In this group, certain of the hagencB 



should also probably be placed (Lagen^). 



Fam. 2. Nodosarina, Chambers nume- 

 rous, arranged in a single straight or 

 curved series ; body jointed. 



Marginulina. Aperture lateral (excentric), 



beaked ; cells turgid. 

 M. raphanus (PI. 18. figs. 7, 9, 10; 8, body 

 freed from shell by acid). 



Fam. 3. Textularina. Cells numerous, 



