20 



PROTOZOA 



filled with sea- water accumulated by endosmosis) and the stiff radiat- 

 ing pseudopodia are directly correlated with the floating pelagic life of 

 the two organisms. All the Eadiolaria are pelagic, and many exhibit 

 this vacuolation ; only a few of the Retioularia are so, and their struc- 

 tural correlation to that habit has only lately been ascertained. 



The Reticularia are almost exclusively known by their shells, 

 which offer a most interesting field for study on account of the very 

 great complexity of form attained by some of them, notwithstand- 

 ing the fact that the animal which produces them is a simple uni- 

 cellular Protozoon. Space does not permit the exposition here of 

 the results obtained by Carpenter in the study of the complex shells 

 of Orbitolites, Operculina, Nummulites, &c. ; it is essential that his 

 work Introduction to the Stvdy of the Foraminifera (Bay Society, 

 1862) should be consulted, and in reference to the sandy-shelled 

 forms the monograph by Brady, in the Challenger Reports, vol. ix., 

 1883 ; and it must be sufficient here to point out the general prin- 

 ciples of the shell-architecture of the Reticularia. Let us suppose 

 that we have an ever-growing protoplasmic body which tends to 

 produce a calcareous shell on its surface, leaving an apertui'e for the 

 exit of its pseudopodia. It will grow too large for its shell and 

 accumulate outside the shell. The accumulated external mass may 

 then secrete a second chamber, resting on the first as chamber 1 

 rests on chamber in Fig. XII. 4. By further growth a new 

 chamber is necessitated, and so is produced a series following one 

 another in a straight line, each chamber communicating with the 

 newer one in front of it by the narrow pseudopodial aperture 

 {a, a\ a^, a?). Now it is possible for these chambers to be very 

 variously arranged instead of simply as in Fig. XII. 4. For instance, 

 each new chamber may completely enclose the last, as in Fig. XII. 

 3, supposing the protoplasm to spread all over the outside of the 

 old chamber before making a new deposit. Again the chambers 

 need not succeed one another in a straight line, but niay be dis- 

 posed in a spiral (Fig. XII. 1). And this spiral may be a fiat coil, 

 or it may be a helicine spiral with a rising axis ; further it may be 

 close or open. All these forms in various degrees of elaboration 

 are exhibited by Miliolidea and various Perforata. 



But the Perforata in virtue of their perforate shell- walls introduce 

 a new complication. The protoplasm issues not only from the 

 mouth of the last-formed chamber, but from the numerous pores in 

 the wall itself. This latter protoplasm exerts its lime-secreting 

 functions ; it gathers itself into coarse branching threads which 

 remain unoalcified, whilst all around a dense deposit of secondary 

 or supplemental shell-substance is thrown down, thus producing a 

 coarsely canalicular structure. The thickness and amount of this 

 secondary shell and the position it may occupy between and around 

 the chambers of primitive shell-substance vary necessarily in dif- 

 ferent genera according to the mode in which the primitive cham- 

 bers are arranged and connected with one another. Calcarina is a 

 fairly typical instance of an abundant secondary shell-deposit (Fig. 

 XII. 10), and it is the existence of structure resembling the chambers 

 of Calcarina with their surrounding primary and secondary shell- 

 substances which has rendered it necessary to regard Eozoon (41) as 

 the metamorphosed encrusting shell of a pre-Cambrian Reticularian. 

 The division of the Reticularia into Imperforata and Perforata 

 which is here maintained has no longer the significance which was 

 once attributed to it. It appears, according to the researches of 

 Brady, that it is not possible to draw a, sharp line between these 

 sub-classes, since there are sandy forms which it is difficult to 

 separate from imperforate Lituolidea and are nevertheless perforate, 

 in fact are ' ' sandy isomorphs of Lagena, Nodosaria, Globigerina, 

 and Eotalia. " It does not appear to the present writer that there 

 can be any insurmountable difficulty in separating the Lituolidea 

 into two groups — those which are sandy isomorphs of the porcel- 

 lanous Miliolidea, and those which are sandy isomorphs of the 

 hyaline Perforata. The two groups of Lituolidea thus formed 

 might be placed in their natural association respectively with the 

 Imperforata and the Perforata. 



The attempt to do this has not been made here, but the classifi- 

 cation of Brady has been adopted. In Biitschli's large work on the 

 Protozoa (9) the breaking up of the Lituolidea is carried out to a 

 logical conclusion, and its members dispersed among the Miliolidea 

 on the one hand and the various orders of Perforata on the other hand. 

 The calcareous shell-substance of the Miliolidea being opaque 

 and white has led to their being called "Porcellana," whilst the 

 transparent calcareous shells of the smaller Perforata has gained 

 for that group the synonym of "Hyalina." 



The shells of the calcareous Reticularia and of some of the 

 larger arenaceous forms are found in stratified rocks, from the 

 Palaeozoic strata onwards. The Chalk is in places largely com- 

 posed of their shells, and the Eocene Nummulitic limestone is 

 mainly a cemei^ted mass of the shells of Nummulitos often as 

 large each as a shilling. The Atlantic ooze is a chalky deposit 

 consisting largely of the shells of Globigerina, &c. 



Class yil. EADIOLARIA, Haeokel, 1862 (63) {Folycystina, Ehr.). 



Characters. — Gymnomyxa in which the protoplasmic body of 



the dominant amoeba phase has the form of a sphere or cone from 



the surface of which radiate filamentous pseudopodia, occasionally 

 anastomosing, and encloses a spherical (homaxonic) or cone-shaped 

 (monaxonic) perforated shell of membranous consistence known as 

 the central capsule, and probably homologous with the perforated 

 shell of a Globigerina. The protoplasm within the capsule (intra- 

 capsular protoplasm) is continuous through the pores or apertures 

 of the capsule with the outer protoplasm. Embedded in the former 

 lies the large and specialized nucleus (one or more). Gelatinous 

 substance is frequently formed peripherally by the extracapsular 

 protoplasm, constituting a kind of soft mantle which is penetrated 

 hy the pseudopodia. A contractile vacuole is never present. 



Usually an abundant skeleton, consisting of spicules of silica or 

 of a peculiar substance called acanthin arrauged radially or tangen- 

 tially, loose or united into a basket-work, is present. Oil globules, 

 pigment, and crystals are found in greater or less abundance in 

 the protoplasm. 



In most but not all Eadiolaria peculiar nucleated yellow cor- 

 puscles are abundantly present, usually regarded as parasitic Algse. 

 Reproduction by fission has been observed, and also in some few 

 species a peculiar formation of swarm-spores (flagellulse) within the 

 central capsule, in which the nucleus takes an important part. 

 All the Radiolaria are marine. The Eadiolaria are divided into 

 two sub-classes according to the chemical nature of their spioular 

 skeleton, and into orders according to the nature and the disposi- 

 tion of the apertures in the wall of the central capsule. 



FiO. XIII. — Thalassicolla pelagica, Eaeckel ; x 25/ CK, central capsule ; 

 £P, extracapsular protoplasm ; al, alveoli, liquid -holding vacuoles in the 

 protoplasm similar to l^ose of Heliozoa, Felomyxa, Hastigerina, &c.; ^5, 

 pseudopodia. The minute unlettered dots are the "yellow cells." 



Sub-class I. Silico-Skeleta, Lankester. 



Characters. — A more or less elaborate basket-work of tangential 

 and radial elements consisting of secreted silica is present ; in rare 

 exceptions no skeleton is developed. 



Okdee 1. PEEIPYL.J;A, Hertwig. * 



Characters. — Silico-skeletal Eadiolaria in which the central cap- 

 sule is uniformly perforated all over by fine pore-canals ; its form is 

 that of a sphere (homaxonic), and to this form the siliceous skeleton 

 primarily conforms, though it may become discoid, rhabdoid, or 

 irregular. The nucleus is usually single, but numerous nuclei are 

 present in each central capsule of the Polycyttaria. 



Fam. 1. SpHiEEiDA, Haeck. Spherical Peripylsea with a spheri- 

 cal basket-work skeleton, sometimes surrounded by a spongy outer 

 skeleton, sometimes simple, sometimes composed of many concentric 

 spheres (never discoid, flattened, or irregular). The central capsule 

 sometimes encloses a part of the spherical skeleton, and often is 

 penetrated by radiating elements. 



Genera (selected). — Mhmosphsera, Haeck. ; Xiphosphaera, Haeck. ; 

 Staurosphsera, Haeck. ; Seliosphsera, Haeck. (Fig. XIV. 14) ; As- 

 tromma, Haeck. ; Haliomma, Haeck. ; Actinomma, Haeck. (Fig. 

 XIV. 17 ; note the sphere within sphere, the smallest lying in the 

 nucleus, and the whole series of spherical shells connected by radial 

 spines) ; Araehnosphsera, Haeck. ; Plegmosphxra, Haeck. ; Spongo- 

 sph^ra, Haeck. (Fig. XVI. 8). 



Fam. 2. Discida, Haeck. Discoid Peripylaea ; both skeleton 

 and central capsule flattened. 



Genera (selected). — Phieodiscus, Haeck. ; Seliodiscus, Haeck. ; 

 Spongodiscws, Haeck. ; Spongurus, Haeck. 



