146 



THE POPULAR EDUCATOR. 



feelers, or else with a fruit-like rounded organ, which, like a 

 fruit, eventually drops off when fully developed. It is true that 

 if we were to attempt to guess at the functions of these organs 

 from this analogy, we should find these appearances very decep- 

 tive. These creatures never derive any nutriment through their 

 roots or stems as plants do, but only through the little mouths 

 at the ends of the branches. Again, the flower-like heads are 

 in function rather like leaves than flowers. Nevertheless, what- 

 ever the function, the general plan of structure and growth is 

 identical, and the likeness was so marked that naturalists were 

 long before they would admit that these creatures were not 

 plants. The animals whose branching stems are so exactly like 

 to plants and shrubs, are microscopic ; but this same resem- 

 blance to vegetables is exhibited, though in a less striking form, 

 in the higher and larger members of the sub-kingdom. If the 

 reader, while peering into the clear waters of a pool left by the 

 ebb of a spring tide, should see a rock covered by a multitude 

 of flower-like heads, each with many circles of purple-tipped 

 tentacles radiating from a common centre like the anthers of 

 the wild rose or the buttercup, all of which seem to float and 

 sway passively with each little eddy he excited, he would cer- 

 tainly take them for sea flowers. Even the common actinia, 

 which is left dry on the rock, collapsed into a dome of jelly, 

 might readily be taken for a flower when, at the first approach 

 :nf the sea, it expands from this bud-like condition into a spread- 

 ing disc, fringed not only with tentacles, but with a circular row 

 of bright blue knobs. 



Otherwise well-educated men, who know nothing of the 

 natural sciences (and the number of these is large), often 

 declare that the lowest animal is but little removed from the 

 highest plant. This, however, is a popular error, and the 

 reverse of this is the case. The true statement is that both 

 kingdoms start from the same point. The simplest and 

 lowest forms of both, especially in their immature condition, 

 are almost identical. At this simplest and earliest stage of 

 development, the plant makes quite as decided an approach 

 towards the typical life of an animal as does the animal make 

 a counter-approach towards the typical life of a vegetable. 

 The young spore of a conferva (vegetable) is locomotive, and 

 moves by the same mechanism as a protozoon. Thus the 

 Rniinal and vegetable kingdoms not only meet at their lowest 

 point, but the vegetable, so to speak, travels more than half 

 way to effect the meeting. From this common point of contact 

 the two kingdoms slowly diverge from one another; but the 

 divergence is so gradual, the angle of divergence is so small, 

 that for some distance they move in an almost parallel course. 

 Now, as the vegetable stops far short of the development 

 of the animal kingdom, we must look for the parallel to its 

 higher forms, not in the lowest animals of all, but in those 

 at some little distance up the scale ; not in the last and 

 lowest division, Protozoa, but in the penultimate sub-kingdom, 

 Ccelenterata. It must, however, be remembered that the 

 analogy to plants is only a parallel. There are no intermediate 

 forms connecting the most plant-like hydrozoon with the most 

 coral-like plant. To find the links of the chain of life which 

 connects them, we must run downward through all the grades 

 of animal life, to mount up again by the different grades of 

 vegetable development. We shall find that though there are 

 fundamental differences, yet the analogy is very strict between 

 Coelenterata and plants in very many respects. 



Though unlimited growth and repetition of parts be the main 

 characteristic of both Crelenterata and the higher plants, some 

 of the former are simple enough. Just as the little pasch- 

 fiower (Anemone pulsatilla) sends up its one blossom in the 

 grass, so does the little fresh-water hydra extend its few 

 tentacles around the mouth end of its tubular body, while 

 it attaches itself, by the other end of the tube, to a water- weed. 



This animal is simply a tube or bag, while its tentacles are 

 narrower tubes, whose hollows communicate with the main 

 one. These are arranged in a circle round the mouth, which is 

 ft perforation in the free end of the tube. The bag is flexible, 

 and composed of two layers of tissue closely adhering to one 

 another. The stuff of which the bag is made is double, and 

 the lining is so like the outer stuff, that the bag can be turned 

 inside out, as Baron Munchausen served the wolf, without 

 deranging its economy. The long arms sway about in search of 

 food. Any little animal unfortunate enough to come in con- 

 iiai t with them, becomes benumbed by some stinging organs 



they contain. They then close around tho prey, and press it in 

 through the mouth into the interior, where its soft parts are 

 dissolved, and its insoluble part is passed out again by the way 

 it entered. 



This short description leads us to remark upon the character 

 which cuts off the Ccelenterata from the higher animals. In tho 

 case mentioned, it will be noticed that the animal is, so to 

 speak, all stomach. The bounding wall of the stomach is also 

 the wall of the body. In the higher animals the food cavity is 

 distinct from the body cavity. These higher animals consist of 

 a tube within a tube. The nutriment derived from food by 

 them is strained through the walls of the inner tube, or other- 

 wise abstracted from it before it can be applied to the main- 

 tenance of the tissues of their bodies. In all the Coelenterata, 

 the food tube is not shut off from the cavity of the body. In the 

 hydra, the stomach is identical with the body cavity ; in others, 

 the stomach is continuous with the body cavity, being only par- 

 tially cut off from it by a circular valve, so that the stomach 

 acts as a kind of porch or vestibule to detain the food a short 

 time, and it is then passed on into the lower part of a tube of 

 equal dimensions. In others, the central stomach divides into 

 radiating hollows, and these divide and subdivide, and often pro- 

 duce a network of fine canals. In these the stomach presents 

 the structure, and has alsw the office of both stomach and 

 blood system of higher animals. All the animals which have 

 stomachs such as we have described, belong to the sub- 

 division of the Coelenterata called Hydrozoa. The other sub- 

 division, called Actinozoa, presents a different arrangement. 

 With them, although the stomach freely communicates with tho 

 body cavity, it is not identical with it, and cannot be said to be 

 continuous with it. Indeed, these animals show an approach 

 to a higher grade by having a stomach within the body wall ; 

 but this tube within a tube is not a perfect one, but opens 

 below into the general cavity of the body. Also a number of 

 partitions run from the body wall to the stomach, so as to 

 maintain the latter in its position, and to divide the body 

 cavity into compartments. This arrangement is well seen in 

 Figs. V. and VI. 



To return to the Hydrozoa. The simple hydra is a locomotive 

 tube, but it fixes itself by one end in a temporary manner. This 

 animal produces young not only from eggs in the ordinary way, 

 but also by putting forth buds from its sides, which, whilo 

 attached to the parent, develop mouths and arms, and then, 

 become separated, being able to live for themselves. 



The hydra, therefore, exhibits functions and tendencies which., 

 when carried to a greater extent in other species, produce very 

 many modifications, and these may be grouped under two types, 

 which, though apparently very different, are, as we shall sec, 

 closely connected with one another. 



1st, tho fixed and branched hydrozoa, with long branching 

 stem, each of whose heads is veiy like the hydra ; and 2nd, the- 

 free swimming hydrozoa, which float at large in the ocean, and 

 have locomotive organs to raise them to the surface and propel 

 them along. 



The animals which range themselves round the first of these 

 types are the most perfect examples of the vegetative habit. 

 The home of the Coelenterata is the water, and almost all except 

 the hydra live exclusively in the salt waters of the ocean. These 

 faced hydrozoa, of course, need not only an atmosphere of water, 

 but a bottom whereon to grow. They are to be found around 

 our coasts, some of them in the pools left by the retreating 

 tide between high and low- water mark. The dredge has brought 

 up some of these animals from great depths, and it is probable 

 that they flourish at still lower levels ; but it is unlikely that, 

 they could live under the enormous pressure exerted by the over- 

 lying waters in the profundity of mid-ocean. Most of these plant- 

 like compound animals are invested with a horny sheath which 

 covers the stem and branches, so that the beautiful patterns in 

 which they grow may be preserved after the soft parts of the 

 animal have been dried up. A collection of such dried specimens 

 gives a far better idea of the animals than a dry herbarium 

 gives of the different species of plants ; for the hard parts being 

 of a stiffer nature, and external instead of internal, the outer 

 form is far better preserved. Some of these hard sheaths or 

 skeletons have at the end of each branchlet a little cup which, in 

 the livf.ig state of the animal, defends the little hydra-like poly- 

 pite(a,s it is called). In another order the sheath ends abruptly, 

 allowing the polypite to be protruded nakedly beyond it. 



