110 THE MICROSCOPE AND ITS REVELATIONS. 



sandstone prevailing through an extensive district in the island of Bar- 

 badoes (Fig. 345). Nothing, however, was known of the nature of the 

 .animals that formed them, until they were discovered and studied in the 

 living state by Prof. J. Miiller; 1 who established the group of Radiolaria, 

 including therein, with the Polycystina of Ehrenberg, the Acanthome- 

 trina ( 505) first recognized by himself, and the Thalassicolla ( 506) 

 which had been discovered by Prof. Huxley. Not long afterwards ap- 

 peared the magnificent and ( epoch-making* work of Prof. Haeckel; 9 and 

 since that time much has been added by various observers to our knowl- 

 edge of this group, which still remains, however, very imperfect. For 

 the following general account of its characters, the Author is indebted to 

 the valuable summary of " Recent Researches in regard to the Radio- 

 laria " lately given by Prof. Mivart. 8 



500. Each individual Radiolarian consists of two portions of colored 

 or colorless sarcode: one portion nucleated and central; the other portion 

 peripheral, and almost always containing certain yellow corpuscles. 

 These two portions are separated by a chitinous membrane called the 

 capsule ; but this is so porous as to allow of their free communication 

 with each other. The yellow corpuscles seem to be true ' cells;' having 

 a regular membranous wall, with protoplasmic contents (including 

 starch-granules), and distinct nuclei; and multiplying themselves by sub- 

 division. But there is considerable doubt whether they are really parts 

 of the animal body, as they have been found in vigorous life when the 

 rest of the animal is dead and decaying; and they are regarded by Cien- 

 kowski as parasites. The pseudopodia radiate in all directions (Plate 

 xviii., figs. 3, 4) from the deeper portion ol the extra-capsular sarcode; 

 they have generally much persistency of direction, and very little flexi- 

 bility; in some species (b\it not ordinarily) they branch and anastomose; 

 while in others they are inclosed in hollow rods that form part of the 

 siliceous skeleton, and issue forth from the extremities of these. A flow 

 of granules takes place along them; and the mode in which they obtain 

 food-particles (consisting of Diatoms and other minute Algae, marine In- 

 fusoria, etc.), and draw them into the sarcode-bodies of the Radiolarians, 

 appears to correspond entirely with their action in Actinophrys and 

 other Heliozoa ( 399). 



501. In most Radiolaria, skeletal structures are developed in the sar- 

 code-body, either inside or outside the capsule, or in both positions; some- 

 times in the form of investing networks having more or less of a spheroi- 

 dal form (Plate xix., figs. 1, 2), or of radiating spines (fig. 3), or .of 

 combinations of these (figs. 4, 5). But in many cases the skeleton con- 

 sists only of a few scattered spicules; and this is especially the case in 

 certain large composite forms or ' colonies ' (Fig. 350) which may consist 

 of as many as a thousand zooids, aggregated together in various forms, 

 discoidal, cylindrical, spheroidal, chain-like, or even necklace-like. The 

 ' colonies ' seem to be produced, like the multiple segments of the bodies 

 of Foraminifera ( 456); by the non-sexual multiplication of a primordial 

 zooid; but whether this multiplication takes place by fission, or by the 

 budding-off of portions of the sarcode-body, has not yet been clearly 



1 ' Ueber dieThalassicollen,Polycystinen\ind Aeanthometren des Mittelmeeres,' 

 In " Abhandlungen der Konigl. Akad. der Wissensch. zu Berlin," 1858, and sepa- 

 rately published; also ' Ueber die im Hafen von Messina beobachteten Polycysti- 

 nen' in the " Monatsberichte " of the Berlin Academy for 1S55, pp. 671-67(5. 



*"Die Radiolarien (Rhizopoda Radiaria)," Berlin, 1862. 



3 " Journal of the Linneean Society," Vol. xiv. (Zool.), p. 136. 



