4U4 



Rhizopoda.- 



-RADIATA.- 



-PORIFERA. 



T~ 



these various removals leave this order of animals now, 

 comparatively speaking, a small one, yet it contains a 

 great number of genera, and the individuals of most of 

 the species are immensely numerous. 



We must content ourselves with indicating some of 

 the leading forms of this interesting order of Protozoa 

 as represented in Plate 1., figs. 1 to 7, inclui'ing the 

 genera Kolpoda, Opiinjoi/lena, Oxylricha, Slylonichia, 

 Discocephalus, Clikimidoclon, and Euplotes. 



Order II.— RHIZOPODA or FORAMINIFERA. 



The species belonging to this order of Protozoa were 

 formerly known to us only by their external coverings 

 or shells, and before the animals were discOT'cred were 

 always considered to belong to the sub-kingdom 

 Mollttsca. They were indeed, from the structure of 

 the shell, generally arranged in the class Cephalopoda, 

 under the name of Pohjthalamia. Dujardiii, however, 

 has lately shown, from bis investigations and discovery 

 of the living animal, that they are nearly allied to the 

 Infusoria. The animals are of a very simple organiza- 

 tion, appearing to be merely a gelatinous mass, or sar- 

 code, with no apparent organs or viscera. Tliey creep 

 slowly by means of a series of filaments or filiform 

 processes of considerable length, which they protrude 

 tlirough the small holes observable in the shells (see 

 Plates 1 and 2.), and which, when watched in motion, 

 appear like a drop of gum flowing along the surface of 

 the substance they move upon. The coverings of these 

 animals are small shells, and consist chiefly of carbonate 

 of lime. The texture, however, varies considerably ; 

 in some being opaqiie, of a close texture like porcelain, 

 and without any external indication of poi-es ; in others 

 being porous, and perforated, especially in the last seg- 

 ments, with a great many small apertures ; and in a 

 third class being transparent as glass. 



The recent species occur in various parts of the sur- 

 face of the globe in immense numbers. The sand of 

 the sea-shore in many places is so completely filled 

 with them, that it appears halfcomposed of these elegant 

 little shells. In the Adriatic Sea four thousand or six 

 thousand have been found in an ounce of sand, and in 

 the West Indies three million eight hundred and forty 

 thousand have been found in the same quantity. If 



we calculate larger quantities, as for example a 

 cubic yard, the amount surpasses all human concep- 

 tion, and we have difficulty in expressing the result- 

 ing number in figures. When we regard in this point 

 of view the whole enormous mass of the sea-coasts 

 of the earth, we must conclude that no other series of 

 beings can, in regard to number, be compared with 

 them. The part they play in creation at the present 

 day is truly wonderful. Banks of sand which impede 

 navigation, obbtr.nct gulfs and straits, and fill up har- 

 bours, are their work ; and along with corals they assist 

 in forming those islands which are every day making 

 their appearance in the warm regions of the great ocean. 

 In former eras of the earth's surface, the part they 

 played seems still more striking. In the carboniferous 

 period enormous masses of limestone in Russia have 

 been found composed almost entirely of a single species 

 of FusoUna; and immense quantities occur in the cre- 

 taceous formations in France. They were still more 

 abundant in the tertiary period. The stones of which 

 the largest pyramids of Egypt are built are so full of a 

 species of Nummuliies, that these extraordinary erec- 

 tions appear to be almost entirely composed of them. 

 The stone of which the houses and buildings of Paris 

 are constructed is so full of a species of Miilolu, that 

 Paris and the villages in the neighbourhood may be 

 said to be built of them. A cubic inch of the stone 

 from the qviarries of Gentilly contains upwards of fifty- 

 eight thousand of these fossil shells, and the beds of 

 which these quarries are composed are of great thick- 

 ness and of vast extent. The actual number of such 

 shells is thus inconceivable. 



A great many species of Foraminifera or Rhizopoda, 

 both recent and foEsil, have been described; but the 

 resear<:hes of the latest authors upon this class tend to 

 throw great doubts upon their value, and give reason 

 to believe that, though individually the Foraminifera 

 are amazingly numerous and abundant, the number of 

 distinct genera and species has been very much exag- 

 gerated. This order has been divided into several 

 families, which are characterized by the arrangement 

 of the chambers constituting the shell. For illustra- 

 tions of these curious creatures we must refer to the 

 magnified figures of the families and genera in Plaies 

 [Rldzopoda) 1 and 2- 



Class V.— PORIFERA (The Sponges). 



The class Porlfera, the last in the zoological series, 

 and the lowest as regards their organization, is com- 

 posed of those substances called Sponges, and to which, 

 amongst many others, the well-known Sponge of com- 

 merce belongs. 



For a long time it was a disputed 'point whether 

 sponges belonged to the animal or vegetable kingdom, 

 and ii is only of late years that the evidence has pre- 

 ponderated in favour of their animal nature. 



Sponge, in the state in which we usually see it, con- 

 sists of a congeries of horny filaments, interlaced in 

 every direction so as to form a most intricate net-work 

 of intercommunicating cells. Imbedded in these fila- 



ments, in the majority of sponges, are a number of very 

 minute needle-shaped, siliceous, or calcareous sub- 

 stances called spiaila. These bodies vary much in 

 form. In some sponges they are simply of a needle- 

 like form, slender and cylindrical, and pointed at both 

 ends. In other instances they have a small knob 

 at one end, whilst the opposite extremity is pointed, 

 giving them exactly the appearance of small pins. In 

 others, again, we find one end transformed into a fork 

 with two or even three prongs ; or the whole spiculum 

 consists of three or four spines of equal length. These 

 spicula appear to be hollow tubes, closed at both ends. 

 This framework with its inclosed spicula, is, however. 



