90 THE MICROSCOPE AND ITS REVELATIONS. 



walls of the piles are thickened at their meeting-angles into solid columns 

 that appear on the surface as tubercles, and are sometimes prolonged 

 into spinous outgrowths that radiate from the central mass, is of very 

 common occurrence in shore-sands and shallow-water dredgings on some 

 parts of the Australian coast and among the Polynesian islands. To the 

 simple form of this genus we are probably to refer a large part of the 

 fossils of the Cretaceous and early Tertiary period, that have been de- 

 scribed under the name Orbitolina, some of which attain a very large size. 

 Globular Orbitolince, which appear to have been artificially perforated 

 and strung as beads, are not unfrequently found associated with the 

 " flint-implements " of gravel-beds. Another very curious modification 

 of the Eotaline type is presented by Polytrema, which so much resem- 

 bles a Zoophyte as to have been taken for a minute Millepore; but which 

 is made up of an aggregation of ' globigerine ' chambers communicating 

 with each other like those of Tinoporus, and differs from that genus 

 in nothing else than its erect and usually branching manner of growth, 

 and the freer communication between its chambers. This, again, is of 

 special interest in relation 4o Eozoon; showing that an indefinite zoo- 

 phytic mode of growth is perfectly compatible with truly Foraminiferal 

 structure. 



484. In Rotalia, properly so called, we find a marked advance towards 

 the highest type of Foraminiferal structure; the partitions that divide 

 the chambers being composed of two laminae, and spaces being left 

 between them which give passage to a system of canals, whose general 

 distribution is shown in Fig. 330. The proper walls of the chambers, 

 moreover, are thickened by an extraneous deposit or * intermediate skel- 

 eton,' which sometimes forms radiating outgrowths; but this peculiar- 

 ity of conformation is carried much further in the genus Calcarina, 

 which has been so designated from its resemblance to a spur-rowel 

 (Plate xvi., fig. 3). The solid club-shaped appendages with which the 

 shell is provided, entirely belonging to the ' intermediate skeleton ' Z>, 

 which is quite independent of the chambered structure a; and this body 

 is nourished by a set of canals containing prolongations of the sarcode- 

 body, which not only furrow the surface of these appendages, but are 

 seen to traverse their interior when this is laid open by section, as 

 shown at c. In no other recent Foraminifer does the ' canal system' 

 attain a like development; and its distribution in this minute shell, 

 which has been made out by careful microscopic study, affords a val- 

 uable clue to its meaning in the gigantic fossil organism Eozoon Cana- 

 dense ( 494). The resemblance which Calcarina bears to the radiate 

 forms of Tinoporus (Fig. 329), which are often found with them in the 

 same dredgings, is frequently extremely striking; and in their early 

 growth the two can scarcely be distinguished, since both commence in a 

 ' rotaline ' spire with radiating appendages; but whilst the successive 

 chambers of Calcarina continue to be added on the same plane, those of 

 Tinoporus are heaped-up in less regular piles. 



485. Certain beds of Carboniferous Limestone in Russia are entirely 

 made up, like the more modern Nummulitic Limestone ( 489), of an 

 aggregation of the remains of a peculiar type of Foraminifera, to which 

 the name Fusulina (indicative of its fusiform or spindle-shape) has been 

 given (Fig. 331). In general aspect and plan of growth it so much re- 

 sembles Alveolina, that its relationship to that type would scarcely be 

 questioned by the superficial observer. But when its mouth is examined, 

 it is found to consist of a single slit in the middle of the lip; and the 



