22 OF THE RHIZOPODA IN GENERAL —RADIOLAUIA. 



apertures for the passage of pseudopodia, and often furnished with radiating elongations (fig. 9). 

 The sarcode body is altogether of an ohve-brown colour, but contains yellow globules, like 

 those of AcanthometrcB. It does not always entirely fill the shell, especially when this does 

 not form a complete casing ; as in the Euci/rtidium, only the upper part of whose bell-shaped 

 " test" is occupied by the body, which is divided into four equal lobes. The pseudopodia of 

 the Polycystina bear a close resemblance to those of Actinoplirys, alike in their gradually 

 tapering form, their isolation from each other, their radiating direction, their indisposition to 

 fusion, and the slow movement of granules along their borders. 



20. Thalassicollina.* — Certain forms oiFolycystina, in which the fenestrations of the 

 siliceous shell are so large and in such close proximity that the solid portion constitutes 

 nothing more than an open network (as is the case with the Didyosoma of Miiller), serve to 

 connect that group with the ThalassicoHina. Of these bodies, which are found passively 

 floating on or near the surface of the ocean, very few forms are yet known, and they are 

 distinguished by Prof. Miiller into the simple and the composite. Of the former we may take 

 as an illustration his Thalassicollamorum (PI. I, fig. 12), which seems very closely to resemble an 

 Adinophry.'i, but presents on its surface, partly imbedded in its ectosarc, a number of composite 

 siliceous spicules (fig. 13), much resembling those of some species of Tethya. In the Th. nudeata 

 of Huxley, the dark spheroidal body is described by him as surrounded by a transparent gela- 

 tinous investment, resembling that which incloses the cells of many Protophytes. The former 

 consists of a spherical vesicle, 1-G5th of an inch in diameter, the wall of which is formed I)v a 

 strong, resisting, and elastic membrane, whilst the interior is composed of fluid, holding 

 in suspension granules of various sizes, with a pale, delicate, nuclear body. In the gelatinous 

 investment many vacuoles are observable, varying in size from l-62d to l-2500th of an inch, 

 the smallest being innermost ; and scattered among the vacuoles of the inner portion, imme- 

 diately surrounding the vesicular body, are many yellow, bright spheres (cells?), about 

 1-1 600th of an inch in diameter, with a multitude of minute granules. From the surface of 

 the vesicular body delicate branching fibrils are seen to radiate through the gelatinous 

 envelope, passing between the vacuoles ; and these are beset with excessively minute dark 

 granules, which are continually circulating among the fibres, but without any definite direc- 

 tion. In the complex type, which is represented by the Thalassicolla pundata of Huxley (the 

 Spharozoum 2}undatum of Miiller), the aggregate mass — which may be either spherical, 

 spheroidal, or hour-glass shaped — is composed of a number of spheroidal bodies, nearly allied 

 to the preceding, imbedded (like the cells of a Palmdia) in a common gelatinous investment 

 (fig. 10). Each spheroid is a cell of from l-200lh to l-250th of an inch in diameter, 

 having a thin but dense membranous wall, and containing a distinct nucleus surrounded by 

 a mass of granules (fig. 11); and it is surrounded by a zone of siliceous spicules, each con- 

 sisting of a short cylinder, from either end of which radiate three or four pointed spines, them- 

 selves beset with pointed processes, closely resembling the spicules of TlaUdtondria. Round 

 each of these spheroidal vesicles, moreover, is seen an aggregation of the before-mentioned 

 small bright yellow spheres ; which are also diffused, though more sparingl)', through the 

 substance of the common gelatinous investment. And through that substance also there are 



* On this family, see especially xi, xxv, lii, lxviii, xciv. 



