89 



FORAMINIFERA. 



FORAMtNIFERA. 



870 



the polype recent discoveries respecting its reproduction by ova, 

 through the agency of medusiform buds, we must conclude that 

 these latter are equally removed from the structureless animals of the 

 Foraminifera. In the preceding argument M. D'Orbigny forgets that 

 the freedom, isolation, and independence, upon which he lays so much 

 stress, are the characteristics of the fixed compound Polypifera, in 

 their embryonic or larval states. Consequently this feature, which in 

 the Foraminifera is normal and persistent, betokens inferiority rather 

 than superiority to the Polypifera, in which aggregation and fixation 

 indicate maturity and a higher development. The argument drawn 

 from their symmetry is of no value. Nothing can be more sym- 

 metrical than many of the sponge spicula ; and in the vegetable 

 kingdom the symmetrical plants (Detmidea) are amongst the 

 lowest forms. 



An additional memoir by Professor Williamson, in 1851 (' Quarterly 

 Journal of Microscopical Science,' vol. i.), afforded other and still 

 more striking evidence of the probable correctness of the views 

 previously enunciated, as furnished by the structure of a species 

 of Faujayintt, and especially showed that the new growths which 

 added to the thickness of the shell were all applied to its exterior 

 and not to its interior, apparently indicating that the gelatin- 

 ous animal had the power of extending itself over the exterior 

 of the shell, or of retreating to its interior at will, reminding us of 

 the movements of the gelatinous envelope in some of the less highly 

 organised Fungiform Corals, (Rymer Jones, 'Animal Kingdom,' 

 p. 19.) In 1845 Dr. Carpenter laid before the Geological Society of 

 London an elaborate memoir on the structure of some interesting 

 fossil forms belonging to the genera Orbitoidea and Nummttlina, 

 which, with the publication of M. D'Orbigny on the Foraminifera of 

 Cuba, constitute the chief additional works that have appeared on 

 this subject. 



The following is the latest classification of the Foraminifera adopted 

 by M. D'Orbigny, and though marked by some serious imperfections, 

 it is the best that has been hitherto published. The five principal 

 divisions are chiefly based on the variations in the arrangement of 

 the successively added segments. 



Order 1. Monoitega. Animal consisting of a single segment. Shell 

 composed of a single chamber. Genera : Gromia, Dujardin ; 

 Orbulina, D'Orbigny ; Oolina, D'Orbigny. 



Order 2. Stichotega. Animal consisting of segments arranged in a 

 single line. Shell composed of chambers superimposed linearly 

 on a single straight or curved axis. No spiral growths : 



Glandvlina, D'Orbigny. Rimulina, D'Orb. 



Nodoiaria, Lamarck. Vaginulina, D'Orb. 



Orthacerina, D'Orb. Marginulina, D'Orb. 



Denlalina, D'Orb. Conulina, D'Orb. 



Frondiculana, Defranee. Paronina, D'Orb. 



LingiUina, D'Orb. Webbina, D'Orb. 





Order. 3. Ifelicotteya. Animal 

 a spiral. Chambers piled 

 forming a spiral volute : 

 Crittellaria, D'Orb. 

 Flabellina, D'Orb. 

 Robvlina, D'Orb. 

 Fiuulina, Fischer. 

 Nonionina, D'Orb. 

 NummuHna, D'Orb. 

 Auilina, D'Orb. 

 Siderolina, Lamarck. 

 Hanerina, D'Orl). 

 Opercvlina, D'Orb. 

 Verltbralina, D'Orb. 

 Polytlomella, Lamarck. 

 Peneroplit, Lamarck. 

 Vendritina, D'Orb. 

 Spirolina, Lamarck. 

 t'yclolina, D'Orl.. 

 J/Uitola, Lamarck. 

 Orbiculina, Lamarck. 



Order 4. Entomostega. Animal composed of alternating segments 

 forming a spiral. Chambers piled up or superimposed upon two 

 alternating axes, forming a spiral : 

 Robertina, D'Orb. Jfeterottegina, D'Orb. 



Attcrigerina, D'Orb. C'aaridulina, D'Orb. 



Amphittegina, D'Orb. 



Order 5. Enallottega. Animal composed of alternately arranged 

 segment* without forming a spiral. Chambers disposed alternately 

 along two or three distinct axes, not forming a spiral : 

 /',>:, iihitvi, D'Orb. Textilaria, Defranee. 



Vutvulina, D'Orb. 



) (Jib. Bolivina, D'Orb. 



I i'Orl>. Mtgrina, D'Orb. 



ii'i-itin, li'Orb. Cuneolina, D'Orb. 



ti'emmulina, D'Orb. 



consisting of segments arranged in 

 up or superimposed on one axis, 



Alreolina, D'Orb. 

 Rotalina, Lamarck. 

 Globigerina, D'Orb. 

 Planoi-biiJina, D'Orb. 

 Truncatulina, D'Orb. 

 Anomalina, D'Orb. 

 Rotalina, D'Orb. 

 Vatrulina, D'Orb. 

 Verneuilina, D'Orb. 

 Bulimina, D'Orb. 

 Uvigerina, D'Orb. 

 Pyrulina, D'Orb. 



Ftn'i'txhin, D'Orb. 



Cauderina, D'Orb. 

 Chryaalidina, D'Orb. 

 Clarulina, D'Orb. 

 Gaudryna, D'Orb. 



Order 6. Agathistega. Animal composed of segments wound round 



an axis. Chambers wound round a common axis, each one 



investing half the entire circumference : 



Uniloculina, D'Orb. Oruciloculina, D'Orb. 



BUoculina, D'Orb. Articulina, D'Orb. 



Fabularia, D'Orb. Sphasroidina, D'Orb. 



Spirolocwlina, D'Orb. Quinqueloculina, D'Orb. 



Triloculina, D'Orb. Adelosina, D'Orb. 



The simplest type of the Foraminifera (Monostega) presents but a 

 single segment, and is illustrated by the Orbulina uninrsa (Jig. 1), 

 which is a small spherical shell with a lateral aperture, the interior of 

 which has been occupied by the living jelly to which the shell owes 

 its existence. The beautifully symmetrical Lngence, or Flask Animals 

 (fig. 2), the British species of which .have been figured by Professor 

 Williamson in the 'Annals of Nat. Hist.,' also belong to this type. 



In the order Stichosteya, as for example the Nodosaria, Denta- 

 Una (fig. 3), the shell advances beyond the simple type of the 

 Monostega by a process of linear budding. The first cell is usually 

 spherical, as in Orbulina, but through the orifice in this primary cell 

 there protrudes as a growth from the contained animal segment, a 

 second segment, usually a little larger than the first, which speedily 

 incases itself in a shelly covering. This new growth is succe'ssively 

 followed by others developed in the same way, until the organism 

 attains to its maturity, when it exhibits a series of cells arranged end 

 to end in a straight or but slightly curved line. 



In the Helicoitega, a large and conspicuous group, the gemination 

 takes place with a spiral bias, producing the nautiloid form of shell 

 which misled the earlier microscopis'ts. Sometimes all the convo- 

 lutions are visible. (Opercnlina, fig. 4.) In others the outer convolution 

 embraces those previously formed, and conceals them (Cristellaria, 

 fig. 5). In a third type all the spiral convolutions are visible on one 

 truncated half of the shell, whilst they are embracing ou the others 

 (Faujasina, fig. 6), thus combining the other two types. Some genera, 

 like the Stichostegous and Heliostcgous orders, develop on tha 

 plan of the latter, up to a certain stage of their growth, when the 

 arrangement of the cells ceases to be spiral and becomes straight, 

 (Spirolina, Jig. 7), as in the Nodosaria: The orifices penetrating the 

 septa and connecting the contiguous segments are sometimes single, 

 and at others more numerous. 



1. Orbulina universa. 2. Lageiia ttriata, var. perluclda. 3. Dent(t!ina 

 commutiis ; Chalk. -1. Opercvlina. 5. Ci'iiteltaria Lyonsii ; Chalk. 6. /''>,/t. 

 fin/Jin. 7. Spirolintt, 



In the Enlomottega the shell is spiral, as in the Helicostega, but 

 instead of each chamber being equilateral, it has a larger and a 

 smaller side, the position of which is alternately reversed as the 

 segments are multiplied. (Cassidulina, jig. 8.) 



In the Enallostega the new segments are arranged alternately on 

 opposite sides of a central line, so as to form two parallel, non-spiral, 

 alternating series (Textilaria, fig. 9), the segments being connected by 

 a single orifice. 



The Agathistega present an entirely different aspect, as well as 

 structure, from the rest of the Foraminifera. They are much less 

 transparent than the majority of the other orders, being composed of 

 a material resembling white porcelain, and which presents a rich 

 amber-brown hue when viewed by transmitted light. They are 

 usually more or less oblong, and as each new segment is equal to the 

 entire length of the shell, it follows that the terminal orifice presents 

 itself alternately at its opposite extremities. Sometimes the new 

 segments are spread out in one uniform plane (Spiroloculina, fig. 10), 

 at other times each new segment instead of being exactly opposite its 

 neighbour, is a little on one side of it ; consequently the chain of seg- 



