HEADING AND ELOCUTION. 



147 





Tho animals represented by the other typo are far more imlo- 

 i. They need no Bco-bottom, and are not confined to the 

 coast, but Huim freely in the Hea fur from any land. The 

 naturalist who during a sea-voyage has energy enough to con- 

 ;i surface-net and trail it from the vessel's stern in fine 

 calm weather, ia sure to be rewarded by obtaining many of these 

 animals. They, however, of coarse, collapse when removed from 

 Icment, and have to be re-immersed in a pail of water be- 

 fort) tlioy exhibit their beautiful structure. We have said these 

 animals swim in mid-ocean ; but how do they swim P They 

 swim by means of two different kinds of organs, one active and 

 the other passive. One order is possessed of a float or bladder 

 which holds air, so that by means of this they can be kept near 

 the surface while attached to their float, and hanging down from 

 it either directly or by the intervention of a long living rope, 

 the polypitoa extend themselves in order to be ready to devour 

 any small prey with which tbjy or their tentacles come in contact, 

 as the whole system is drifted by wind and current along the 

 surface. Other free-swimming hydrozoa have, in addition to or 

 in lieu of floats, flexible and contractile cups, to the outside of 

 which the strings of polypites ore slung. These cups the 

 Animal causes to bo suddenly contracted by bringing the sides of 

 the cup forcibly together, and ao driving out the water. This 

 motion causes the cup to be driven in the direction towards 

 which the bottom of the cup is turned, and so to drag after it 

 the chain of polypites. The cup is then allowed slowly to dilate 

 by the elasticity of its substance, and is then again forcibly 

 contracted. It may bo conjectured that these swimming organs, 

 though they have a locomotive function, are not used to effect 

 locomotion in any definite direction, except it be upward or 

 downward. Xo doubt, the instinct of these creatures, low as it 

 is, induces them to seek the surface in fine calm weather, and to 

 sink to stiller depths when rain and storms come. These again 

 may also be used to effect change of place when the waters are 

 stagnant ; but, of course, the animals so moved do not pursue 

 their prey. Trailing as a car from its balloon, these creatures 

 are floated through the ocean and find their food haphazard. 

 The question arises, how do these soft and feeble creatures secure 

 live things which have much greater power of locomotion than 

 themselves, and whoso struggles, one would think, would be suffi- 

 cient to tear the delicate arms of their captors quite away ? Their 

 power of capture is rather chemical than mechanical. All the 

 Ccelenterata have small organs embedded in their tissues near 

 the surface, called thread-cells. They are especially numerous in 

 the tentacles, and consist of small double-walled sacs. The outer 

 HOC bursts under the slightest excitement or touch, and a long 

 fine thread, which lay coiled up between the two sacs, and is 

 attached to the end of the inner sac, is darted forth with a 

 rapid motion. This thread is a sting which conducts poison 

 into the body of the animal it touches ; but whether the poison 

 is contained in the inner sac, and is passed up through tho 

 thread, or whether it lies between the sacs, does not seem to bo 

 ascertained. Whatever the method, the fact of the stinging 

 sensation produced by the thread-cell is demonstrable enough. 

 Not only are the little animals which come in contact with the 

 arms of the hydrozoa seen to become benumbed and helpless, 

 but even upon man the stinging is sometimes severe. One of 

 the largest of the float-bearing hydrozoa, wlu'ch is a very con- 

 spicuous object at sea, not only from its comparatively large 

 size, but also from the beauty of the rainbow tints which shine 

 forth from its float, is called the Portuguese man-of-war. This 

 animal furnishes the rough-and-ready seaman with a means of 

 gratifying his taste for practical jokes. The Portuguese man- 

 of-war is put in a pail, and the novice is induced to touch it, 

 when ho not only becomes tho victim of the discharge from the 

 man-of-war, but also of a broadside of laughter from the crew 

 pf his own vessel. Aristotle was so well acquainted with the 

 stinging power of these animals, that he called them Acalephaa 

 (or nettles). 



There ia another order of free-swimming hydrozoa, which 

 differ from those described in that their swimming cup is single, 

 and instead of having the living rope with its polypites and 

 tentacles slung on to its outside, has a single polypite suspended 

 from the centre of its under or concave side, while the tentacles 

 are arranged at regular intervals round the margin of the cup. 

 The mouth of the polypite leads into a central stomach, which 

 sends out radial canals to run to the margin, and these are there 

 Connected with a circular canal, which runs round the lip of the 



cup. Theo are called Mediuwj, from Medusa, whom Neptene 

 loved for her golden lock*, which were afterward* converted iato 

 headed snake*. Whether tho Urge round disc-like bodies of these 

 creatures, which every one must have Men who ha* been by the 

 seaside, bent represent the Gorgon before or after the transforma- 

 tion, must be left to the imagination of each individual. The** 

 creatures are also remarkable because they present the first 

 indications of thone organs of senaa which become so com- 

 plicated in higher animals. Around the margin of the cop or 

 bell of some Medossa, sometimes sitoated just opposite each 

 tentacle, and sometimes between these, sometimes protected by 

 a kind of flap and exposed nakedly on a slight projection, 

 are found a number of little roundish bodies. These generally 

 consist of a little vesicle with a nerve ending behind it, and r. 

 spot of bright-coloured pigment behind this again. Other of 

 these bodies enclose in a vesicle a little crystal of carbonate ot 

 lime. It ia thought that the first are adapted to receive im- 

 pressions of light; and the last, vibrations of sound. In fact, they 

 are the simplest eyes and ears known in the animal kingdom. 



Another order of the hydrozoa are like the simple hydra in 

 that they have a disc by which they can fix themselves in a 

 temporary way, but they differ from these animals in that they 

 possess an organ expanded round the polypite, called an umbrella. 

 This organ they can use as a swimming organ when they detach 

 themselves. 



Thus the Hydrozoa have been divided into seven orders, thus 

 defined : 



1. Hydridce. Animals characterised by a single locomotive 

 polypite. 



2. Corynidce. Animals, simple or compound, which are fixed, 

 and have no cups developed from the hard outer layer to protect 

 the polypitea. 



3. SertularidoB. Compound animals, with protective cups to 

 their polypites. 



4. CcdycopharidaB (Cup-bearers). Free-swimming animal*, 

 with an undivided string of polypites slung to the outside- of 

 one or more swimming cups. 



5. Physophoridce (Float-bearers). Like the last, bat baring 

 floats. 



6. Medu&idee. Animals with a single polypite hanging from 

 the centre of a large cup-like disc. 



7. Lucernaridw. Animals characterised by an umbrella. 

 These would seem at first sight to be good marked character*, 



by which to distinguish the orders ; bat in reality these orders 

 are only provisional, and their unsatisfactory character will illus- 

 trate how futile it is to endeavour to classify animals before we 

 know their whole life-history. It is found that some of tiie 

 flower-like heads of the orders 2 and 3 become developed into 

 animals precisely like those belonging to the order 6, and then 

 drop off and swim away as complete Medusae. Farther, somo 

 of the order No. 7, which swim freely, give birth to young that 

 become permanently fixed, and grow for some time like animal* 

 of the second and third order. The circle of life, howo 

 completed in both cases, for the free-swimming Medusas have 

 young which grow into compound animals, like the stock from 

 which they were derived, and the fixed young of the Luccrnaridar, 

 when exposed to fresh or unfavourable conditions, have their 

 tubular bodies transversely divided into a number of saucer, 

 shaped discs, which one by one become detached, and swim 

 away to become developed into an umbrella-bearing Luoernarid. 



The phenomenon above described is called an "alternation of 

 genarations," but the phrase is an objectionable one. 



In the engraving, two forms (Figs. VH., VTJI.) taken from 

 the other class, which is called Actinosoa, are given, in ori.-r 

 to show the contrast between them and the Hydrozoa ; bat we 

 must leave tho description of them for another lesson. 



READING AND ELOCUTION. XVIII. 



ANALYSIS OF THE VOICE (eontin uI). 

 RULES ON EXPRESSIVE TONES 



Rule 4. Atce has usually a "suppressed" force, a "very 

 low " note, and a " very slow " movement. Solemnity, rettr- 

 enc, and sublimity have a " moderate " force, a " low " noU, 

 and a "slow movement" All four of these emotions an 

 nttered with " effusive medial stress," and dwp, but " pure," 

 " pectoral quality ; "together with a prevalent " monotone-" 



