THE POPULAR EDUCATOR. 



appended a typical and familiar example or examples to each 

 class ; so that the student may have a concrete idea of each, 

 which will at least assist his memory, and perhaps suggest much 

 of the structure of the class to which it is appended. The deri- 

 vation of the names is also given, so that these terms, which are 

 so useful for the purpose of expressing definitely each class, may 

 not be considered as mere senseless jargon : 



TABLE OF THE SUB-DIVISIONS OE CLASSES OP THE ANIMAL 

 KINGDOM. 



Protozoa. Although we have given under the branch Protozoa 

 a number of classes such as are to be found in treatises on these 

 animals, the characters upon which these classes have been 

 formed are so very unsatisfactory that it is better to give a 

 general description of these animals as a whole. 



In all the animals higher than the Protozoa tissues are found 

 which have a definite complex structure, the most constant and 

 the ultimate element of which is a cell which is a little round 

 or oval bag with fluid contents, and often a more or less solid 

 minute lump, called a nucleus. Many of the parts of the higher 

 animals are entirely made up of immense multitudes of these 

 cells closely pressed together, and none of these animals, when 

 perfect, but exhibit a cellular structure in some of their parts. 

 In the Protozoa, however, no structure, cellular or other, has 

 been found. We may take as a type of the simple Protozoa the 

 animal called the amoeba, which is found in fresh water-ditches. 

 It seems to consist of a little elastic mass of jelly-like consistence, 

 without cells or structure of any kind. If this little lump of 

 glue-like matter be placed in a watch-glass under water, and 

 observed with a microscope, it soon protrudes from its rounded 

 exterior projections, which become extended into what may be 

 called temporary limbs. With these it moves about, fixing some 

 in the direction in which it is travelling ; it then draws the 

 remainder of its body towards them, while they grow shorter 

 and disappear in the general mass, and fresh ones are put forth 

 from any other part of the body, as the animal wills. The 

 higher animals are bound together by membranes, and moved 

 by muscles; but how these little creatures are held together and 



move is a mystery, since they have no muscular tissue, and no 

 cellular membranes. 



The mode of eating, if so it may be called, is equally simple 

 and strange. Some of them swallow almost every substance 

 they come near which is not too big to be surrounded by their 

 elastic bodies. They, however, have no mouths, gullets, or 

 stomachs, but they first gather their false limbs around the 

 food, and then press it into the substance of their bodies, or 

 extend themselves around it until they close it in. What- 

 ever good can be obtained from it is dissolved, and then it is 

 squeezed out again. A creature nearly allied to amoeba has 

 received the appropriate name of Pamphagus mutabilis, or the 

 ever-changing universal swallower. The temporary projections 

 are very changeful in the same animal, but they are very diffe- 

 rent in character in the different animals. In the amosba they 

 are few, large, and thick ; but in the actinophrys they are long, 

 thin, tapering, and stretch away in all directions, like the rays of 

 light from the sun when veiled or surrounded with thin clouds. 

 Like these sunbeams they neither unite nor branch, hence the 

 animal is called the ray or sun animalcule. Another form, 

 called Gromia, sends out projections which branch and re-branch, 

 and run into one another wherever they meet. All these tem- 

 porary limbs are called pseudopodia, which means false legs ; and 

 the possession of them has given them the name of root-footed 

 animals, because of their fancied resemblance to the roots of a 

 tree. The body substance from which they are formed is called 

 sarcode. This term sarcode is a good illustration of the use and 

 the necessity of technical terms. The Greek word o"ap| (sarks) 

 means flesh, and the term sarcode is well applied to express the 

 fleshy substance of these animals ; but if the English word flesh 

 had been used, it would convey a totally false idea, because, as we 

 have seen, it is the main peculiarity of these animals that their 

 substance is unlilce flesh. Thus, by taking the word sarcode, 

 and applying it to that kind of fleshy substance possessed by 

 Protozoa as distinguished from all other kinds of flesh, we have 

 established a definite and useful term. The body substance of 

 these simple animals is not, however, wholly alike throughout. 

 Sometimes it breaks up into fine fragments in the internal 

 parts, and becomes granulated, as it is called, and sometimes 

 it exhibits a great many holes or cavities. These are, however, 

 temporary modifications. On the other hand, there are usually 

 to be found in the substance of the sarcode two kinds of con- 

 stant organs which retain their places. One of these is called the 

 contractile vesicle, which keeps constantly slowly growing and then 

 suddenly collapsing. The other is a knot of opaque matter, called 

 the nucleus. The former is probably a respiratory organ for pump- 

 ing fresh aerated water into the deeper substance of the body 

 from the outside, and the latter is the reproductive organ. 



Thus we see that the sarcode is able to perform a great many 

 functions, such as locomotion, secretion, deglutition (swallow- 

 ing), and digestion, although the means whereby it does all 

 this is unknown. The nature of the sarcode is now receiving the 

 attention of the patient German investigators, and it will proba- 

 bly turn out that its structure is not so simple as was once sup- 

 posed. However, these animals are good examples of the want 

 of differentiation of parts, as we should naturally expect, since 

 all naturalists have placed them lowest in the animal scale. 



Hitherto we have confined ourselves to the description of 

 the simple forms of the Protozoa, but many of these animals 

 have the power of reproducing, by buds from their sides, fresh 

 lumps of sarcode like the original one, and these remain in 

 connection with one another, and so form very complex animals. 



These complex forms usually secrete on their outsides a shell 

 whose form is often regular, complicated, and beautiful, in pro- 

 portion as the process of budding is regular and symmetrical. 

 We indicate some -of the methods by which budding produces 

 complex shells : 



1. Suppose the little lump of sarcode send forth a narrow 

 neck on one side, and another little mass is developed at its 

 end ; and then this should send forth another neck in the same 

 straight line with the first, and the process be continued while 

 a shell is secreted to envelope the whole, it will then be in the 

 shape of a beaded rod. 



2. If the second neck be not in the same straight line with the 

 first, but a little to one side and in the same plane, and this mode 

 of growth go on, a shell like that of the nautilus will be produced. 



3. If, in addition to being on one side of the line of the first, 

 it be raised a little out of its plane, this method will produce a 



