RALIOLAE1A. 



343 



ectosarc and a granular and highly-coloured endosarc (sometimes bright red), enclosing a large central 

 body with a membranous envelope. 



Vacuoles, and many minute yellow bodies the latter defined by Wallich as " sarcoblasts," 



such as occur in very many other Rhizopods, and serve as their ovules, are also present ; and there is 

 the usual kind of protoplasmic circulation. In many forms there is a silicious skeleton, either of 

 interlacing spicules, or of connected rods and meshes, or a perforated spherule, constituting under 

 various modifications, exquisitely beautiful crystal basket-work, lattices, or trellises, surpassing even 

 the perforated, ivory-nested capsules of the neatest and most elaborate Chinese carvin. In tliis 

 character of silicious basket-work, they re- 

 semble those Racliolarians which possess no 

 nucleus or contractile vesicle, and are specially 

 known as Polycistina. * 



XXXIX. Of the Plagiacanths, as defined 

 by Dr. "Wallich, the Acantliometra^ (Fig. 7) 

 heads a numerous and important group. 

 Xiphaccuithci^ (Fig. 8) is one of them, and has 

 a silicious skeleton of twenty long, sharp, 

 regular, radiating rods or prickles, the bases 

 of which fit neatly together in the central 

 capsular body. Just within the surface of 

 the body, and parallel to it, each gives off 

 symmetrical cruciform branches, which consti- 

 tute altogether an open spheroidal lattice- work. 



XL. Stylodictya (Fig. 9) belongs to a 

 series of more or less discoidal forms, com- 

 posed of two parallel, perforated, or reticulate 

 plates, coalescing round the margin (from 

 which spines project at regular distances), and 

 separated elsewhere by an intermediate series 

 of concentric or spiral rings. 



XLI. Tiialassicolla\\ is one of the marine 

 nucleated Racliolarians without a skeleton. Acanthodesma,^ an allied form, has a loose network of 

 spicules for a skeleton ; and, in other forms belonging to this group, there are various modifications 

 of rods and rays. 



XLII. In the Collosphcera** and in Sphcerozoum, ft numerous minute nucleate indi- 

 viduals are associated in a relatively large gelatinous mass. In the latter species, each zooid 

 has silicious spicules, but in the former each has a simple perforated or fenestrated spherical 

 skeleton. 



XLIII. Artificially arranged among the Rodiolaria, on account of the structure of their 

 skeleton, are the Polycistina ; but Dr. Wallich recognises in them neither central nucleus nor any 

 contractile vesicle, sarcode not differentiated into endosarc and ectosarc, some vacuoles, the 

 pseudopods frequently anastomosing, and showing the usual kind of circulation. Their silicious 

 skeleton, generally globular, is variously trellised, and sometimes composed of two, or even three, 

 concentric basket-balls, supported and separated by few or many long radiating spicules, passing from 

 the centre to beyond the surface. These rays commence from a central base (" omphalostyle"JJ of 

 Wallich), either symmetrical in a spherical chamber, in his " Cyclolina " (circular), with Haliomma, 

 Ainphidisciis,\\\\ and Astronun((*\ for types, or asymmetrically, as in his " Monodina " (single), with 

 Podocyrtis for their type. 



Fig. 7. ACAXTHOMETRA ECHINOIDES. 



Highly magnified. (After Claparicle and Lathman.) 



Greek, jwhix, many ; riste, a box. 



Greek, ;riphf>#, a sword ; acantha, a thorn. 



Greek, thalcwsa, the sea ; colla, glue, jelly. 

 * Greek, colla, jelly ; spkaira, a sphere. 

 J Greek, omphalos, a navel ; styJos, a column. 

 ii Greek; amplii, round-about; discos, a u^uoit. 



t Greek, acantha, a thorn ; metron, a measure. 

 Greek, stylos, a column ; diktyon, a net. 

 " Greek, acantha, a thorn ; desmos, a chain. 

 ft Greek, sphaira; zoon, an animal. 

 >! Greek, hals, the sea ; omma, an eye. 

 1iU Greek, astron, a star ; omma, an eye. 



