350 



NATURAL HISTORY. 



FigS. 29-33. FORAMIXI"EUAL SHELLS. 



(After d'Ofligny.) 



>, Plnnortiulina mediterranonsis; so, Penerop'is 

 (IX'iulntiua) arbuicula ; 31, Cnirarina defraiicii ; 



TS. lluliinina marginata; 33, Uvigerina pj-.trnisi-a. 

 Fig?, at, 33 aro figured with the aperture down- 

 wards. 



buildings have been constructed such as the Cathedral of Gerona and some of the Pyramids 



of Egypt. Fiisulina (distaff) is a spindle-shaped Nuinnmlitid forming masses of limestone of 



Carboniferous age in Russia and North America. This form, A Iveolina, and Loftusia, resembling 



one another in shape, belong to quite different groups ; an example of the imperfection of d'Orbigny's 



classification based on the shape of shell and setting on of the chambers. 



In many of the Foraminifera, especially the Porcellana, the chamber- walls merely tent over the 



sarcode, whether thread-like, beaded, folded, or spiral ; the edges of the new chamber resting on 



the surface either of the object to which the Foraminifer is 

 attached, or on a former whorl of the shell. In more highly- 

 developed hyaline species, each segment of sarcode becomes 

 wholly coated with perforated shell-matter, except where it is 

 attached by the stolon to the previous segment, and where 

 it gives off a new bud. Further, the sarcode is thrown back 

 over the already formed chambers more or less freely, and 

 the test gets thickened, and sometimes ornamented with supple- 

 mental shell-growth. But a most important feature in the 

 best kind of these shells (Nummulites, Polystomella, Rotalia, 

 Calcarina, &c.) consists of a system of vessels, or canals, 

 formed between the consecutive chambers of such well-coated 

 kinds, and continued in a spiral manner along the upper and 

 lower edges of the chambers, and communicating either directly 

 with the surface (Polystomella), or through a reticulation of 

 similar vessels in the thickened edge or " marginal cord " of 



the shell. These vascular portions have been termed the "intermediate skeleton,'' with its "canal- 

 system," and evidently permit of free sarcodic communication between the early innermost segments 



and the outside (Fig. 34). 



It is very doubtful to some if the Foraminifera and the marine Radiolaria use their pseudopods 



for catching living prey ; and it has been suggested that they obtain nourishment by absorption 



of nitrogenised aliment from the sea-water. The similarity, 



however, of their pseudopods with those of prey-catching 



Reticularia supports, by analogy, the idea that they take 



organic particles as food. 



In some cases young Foraminifera, resembling what 



must have been the earliest stages (primordial segments) 



of the parent, have been found within the shell of an 



adult individual, and too large to escape by the stolonal 



aperture. The mother, then, would be at least partially burst 



for their escape. In other cases such a brood has been 



seen outside and around the mother, possibly having been 



emitted in an imperfect state. There seems to be no doubt 



that the sarcoblasts so often present, and looking like ovules, 



may be the sources of young broods. It has been remarked 



by Williamson that some twin monstrosities, as double For- 



aminifers, beginning in one primordial chamber, may indicate 



that "fission" is one method of reproduction with these 



creatures under some circumstances. 



XLIX. Many animalcules formerly classed among the 



Infusoria (which are an important group of the Protozoa], especially Monas and its allies, have 



of late years been recognised as belonging to a different protozoan group, more nearly allied to 



the Rhizopods, inasmuch as at some period of their existence they are in an Amoeboid condition, if 



not living as actual Amoebce. Their typical form is a nucleated corpuscle, with a vacuole, and an 



external thread-like appendage, or tail-like lash. Hence they have been grouped as the Flagellata* 



* Latin, flagettvm, a little whip. 



Fig. 34. SECTION OF THE SHELL OF ROTALIA 

 SCHROZTERIANA, NEAR AND PARALLEL TO 

 ITS BASE. (After Williamson and Carpenter.) 



Sliowincr n a, tli<> radiating intcrsepta! canals i Ij, their 

 internal bifurcations ; c, a transverse branch , d, the 

 tubuliferoiis wall of the chambers. 



