CHAMBERS'S INFORMATION FOR THE PEOPLE. 



Zebra, Equus zebra; and the Ass, Equus asinus. 

 A number of genera with more common characters 

 are usually grouped as an order: for example, the 

 Ruminant animals, as cattle, deer, &c. form an 

 order. Sometimes, however, a group of genera, 

 with certain characters in common, is called a 

 family; for example, the crow, jay, magpie, chough, 

 &c. form the family Corvida. In these instances, 

 a group of families forms an order. To a com- 

 bination of orders, the termcfass is applied for 

 example, birds, fish, reptiles. Then we come to 

 characters still more general, according to which 

 the entire animal kingdom has been subdivided 

 into six sub-kingdoms. These have also been 

 called morphological types, and are, as it were, 

 the great ground-plans upon which the Divine 

 Architect has constructed all animals. Thus, we 

 have Sub-kingdoms, Classes, Orders, Families, 

 Genera, Species, and Varieties, each term in 

 succession being applicable in a more and more 

 particular way than its predecessor. 



The six sub-kingdoms or morphological types 

 of the animal kingdom are : 



I. PROTOZOA for example, amoeba, sponges, infusoria. 

 II. CCELENTERATA for example, sea-anemones, sea- 

 firs, corals. 



III. ECHINODERMATA for example, sea-urchins, star- 



fish. 



IV. ANNULOSA, or Ringed Animals for example, in- 



sects, spiders, worms. 



V. MOLLUSCA, or Pulpy Animals for example, sea- 

 mats, oysters, cuttle-fish. 



VI. VERTEBRATA, or Back-l>oned Animals for ex- 

 ample, fishes, birds, reptiles, and man. 



stance and the outer layer ; there is neither mouth, 

 contractile vesicle, nor nucleus. So far as we as yet 

 know, the Monera in no case multiply by sexual 

 reproduction. A portion separates as a bud, or an 



L SUB-KINGDOM PROTOZOA. 



The Protozoa (Gr. protos, first, zoon, animal 

 the beginnings of life) are usually minute, and 

 many of them can be seen only by the aid of 

 the microscope ; but sometimes they are of con- 

 siderable size, for example, the sponges. They are 

 formed of a jelly-like substance called 'sarcode,' 

 or 'protoplasm,' which exhibits little or no trace 

 of structure, resembling closely raw white of egg, 

 more or less firm. In most is found a small 

 solid body, the ' nucleus,' which, from recent 

 observations, appears to be an ovary ; and near 

 this, one or tv/o still more minute particles, the 

 ' nucleoli,' which seem to be cells containing fer- 

 tilising filaments. In many, contractile vesicles 

 have been observed, spaces filled with a clear 

 fluid which is driven by a contraction of the wall 

 of the cavity through invisible channels in the 

 body substance. Most are nourished by absorp- 

 tion through the general surface. They do not 

 possess a nervous system or organs of sense, 

 neither is there any distinct digestive system. In 

 nearly all, a mouth is absent, but it is present in 

 one group. They are nearly all aquatic. 



CLASS I. THE MONERA. 



The Monera are the simplest of living beings. 

 They consist of structureless, homogeneous, semi- 

 fluid protoplasm, sometimes so soft and transparent 

 that one can detect it only by its not mixing with 

 the outer water. In this group there is no marked 

 difference in consistence between the inner sub- 



132 



Protomyxa aurantiaca (after Haeckel). 



individual or a separated part contracts into a 

 round ball, and becomes covered by a transparent 

 layer ; the central mass then breaks up into, a 

 multitude of grains. Finally, the outer covering 

 bursts, and each of the grains becomes a separate 

 'moner' of the same species. Notwithstanding 

 their extreme simplicity, the Monera present 

 specific and even generic distinctions. They differ 

 in colour : Protomyxa aurantiaca, described by 

 Professor Ernst Haeckel, is bright orange. They 

 differ likewise in habit Myxodictyum sociale of 

 the same author lives in a colony, each of the little 

 round moners being attached to a number of 

 others by spreading sarcode threads. 



A large part of the bed of the North Atlantic at 

 great depths is covered with a calcareous sediment 

 composed almost entirely of the broken shells of 

 Foraminifera, the group of Protozoa to be next 

 mentioned. This lime-mud is usually slightly 

 tenacious, as if a little size were mixed with it. On 

 putting it under the microscope, this glairy matter 

 separates into irregular strings, which shew move- 

 ment This would seem to be a form of the 

 Monera, even more simple than those which 

 have a definite shape. To this ' Urschleim ' of the 

 Atlantic chalk mud, Professor Huxley has given 

 the name of bathybius. 



CLASS II. RHIZOPODA. 



Gromia is the type. The sarcode body is 

 inclosed in an egg-shaped membranous shell or 

 ' test,' which has a single opening at one end, 

 whence issue long prolongations of its body. 

 These are termed pseudo-podia (false feet). They 

 have no limiting wall, but seem just to flow 

 along in the water, and when two come in con- 

 tact, they flow together. It has no mouth, but 

 obtains its food by throwing out its pseudo-podia, 

 which, when they encounter any substance, such 

 as a minute diatom, gradually close round it, and 

 then pull it into the interior of the shell, where it 

 is digested by the sarcode ; and then the indi- 

 gestible portions are expelled through the opening 

 in the shell. 



