OF THE RHIZOPODA IN GENERAL :—RAmOLARIA. 21 



forth from one extremity, which is destitute of any membranous envelope; thus affording a 

 transition towards such genera as Eughjplia (fig. 5), in which the body is inclosed in a flask- 

 shaped membranous " test," often elegantly sculptured on its surface, and having a wide 

 orifice from which the pseudopodia are put forth. 



18. ACANTHOMETRINA.* — The siliccous skeletons of the Acatliomeirina, which are all 

 marine, t consist of a number of elongated spines, which meet in a common centre, and 

 radiate from this with great regularity (PI. I, fig. 7). These spines arc hollow, and the canal 

 by which each is traversed opens-out near its base into a furrow, by which a pseudopodian 

 process of the body of the animal gains access to its interior, to issue forth again at its apex. 

 There are, however, many pseudopodia not thus inclosed, which strongly resemble those of 

 Actinophnjs in their appearance and their action. The body is spherical in form, and occu- 

 pies the spaces left between the bases of the spines, which in some species widen-out so 

 much as to join each other by their edges at some distance from the centre (fig. 8), thus 

 dividing the interior of the sphere of sarcode into pyramidal segments. The ectosarc seems 

 to have a more definitely-membranous consistence than in Aclinoplirys ; but it is pierced bv 

 the pseudopodia, whose convergence may be traced from without inwards, after passing 

 through it, and it is itself enveloped in a layer of less tenacious protoplasm resembling that 

 of which the pseudopodia are composed. The cndosarc contains a number of yellow cell-like 

 globules, resembling those of Thalassicollm, having a thick peripheral layer and a central 

 cavity. These are rendered brown by tincture of iodine, and are blackened by the sub- 

 sequent action of sulphuric acid, whilst the rest of the body assumes a deep yellow colour; 

 on the other hand, they are turned green by hydrochloric acid. 



19. PoLYCYSTiN.\.t — The very numerous group of Pohjcystina, whose skeletons furnish 

 to the microscopist so many objects of the highest interest for their varied beauty, is also 

 entirely marine ;§ and is distinguished from the foregoing in having the body itself more or 

 less completely inclosed in a siliceous envelope, fenestrated or perforated witii numerous 



* On tins family, see especially xi, xxv, lxviii. 



f The Acanthometra echinoides is described by MM. Claparede and Lachin.inn (sxv, p. 460) 

 as extremely common on some parts of the cuast of Norway; being brought in abundance by westerly 

 winds into the fiord of Bergen, from which it disappears when the wind changes; but being always 

 to be found at Glesnaitholm, which is nearer the open sea. To the naked eye, it presents itself as a 

 crimson-red point, the diameter of its body (not including the spicules or pseudopodia) being 

 0'15 roillira., or 0-006 inch. This colour is seen under the microscope to depend upon the pre- 

 sence, in the central part of the body, of a mass of pigment, which, when viewed by transmitted light, 

 is no longer crimson, but reddish purple. Acanthomelrie do not seem to have yet been discovered near 

 our own shores. As they are undoubtedly inhabitants of the North Sea, they should be looked-for on 

 our eastern coast when the wind blows towards the shore. 



I On this family, see especially xi, xxv, xli, xlii, lxviii. 



§ They are best known as the " Fossil Infusoria of Barbadoes ;" a large proportion of a Sandstone 

 that prevails through an extensive district of that island, being composed of the siliceous skeletons 

 of Polycystina, more or less firmly united together by a calcareous cement. 



