part of the winter in a dormant state. They are arranged in four orders. The Tortoises (Chelo'nia) have a covering consisting of an upper and under shell, joined at their sides into one, which permits only their head and other extremities to be extended without it. They have no teeth but their jaws are armed with a tough horny substance which supplies their place. The order of Lizards (Sau'ria) includes a very considerable variety. The greater part of them have four feet, but a few are possessed of only two. They have nails and teeth, and their skin is covered with scales. Among them are the crocodile, the alligator, the chameleon, the true lizards and the dragons. The crocodile is the most celebrated. It is from twenty to thirty feet in length including the tail, and is covered with a coat of scales, which on the back form an armour proof against a bullet, and have an appearance like that of carved work. The Serpents (Ophidia) are distinguished by their long and slender bodies without limbs, and by the great extensibility of their jaws, mouth and throat. They are divided into the venomous and those that are not venomous. The number of the latter is the greatest and includes the largest animals. The venomous serpents are generally armed with fangs for the specific purpose of infusing poison into the wounds they inflict. When the tooth pierces the flesh of any animal, the poisonous fluid is injected into the opening. When broken or injured, these fangs are renewed, and when not employed, are hidden from the sight by a fold or projection of the gum. Serpents cast their skins annually, and the beauty and lustre of their colours are then highly augmented. The reptiles of the fourth order (Batrach'ia, frog, salamander, &c.) are principally remarkable for a transformation which takes place in their offspring after leaving the egg. When first hatched, they are strictly an aquatic animal, and capable of breathing and living only under water. In this state they are seen by thousands, of a dark colour, with round bodies, swimming about in brooks and small ponds. After a certain period, their form and structure are altered and they become at once animals capable of breathing only in air. Fishes being destined to inhabit only the water, are provided with organs and a structure adapted to the element in which they reside. Since they cannot breathe pure air, they STRUCTURE OF INSECTS. 221 have a peculiar modification of the organs of respiration and circulation. A current of water is constantly passed over the gills by the action of the mouth of the animal, and by means of the air it contains, exerts an influence over the blood circulating in them, and produces the same changes in it as are produced in the lungs of other animals by the air they breathe. A few fishes, one of which is called the torpedo, are possessed of a very remarkable means of defence, which consists in the power of inflicting upon whatever living creature comes in contact with them, a powerful electrical shock. These shocks are so powerful, that in South America, horses driven into the pools which some fishes of this kind inhabit, have sometimes been stunned and even killed. The shocks become weaker and weaker upon continued repetition, till the animal is exhausted, and loses for some time the power of producing any effect. QUESTIONS.-1. What is said of reptiles? 2. Describe the first order. 3. The second. 4. The third. 5. The fourth. 6. Describe the organs of respiration and circulation in fishes. 7. What remarkable means of defence have some fishes? [NOTE. Fishes are divided into orders and genera, according to certain differences in the formation, structure, and situation of their mouth, gills, gill-coverings, fins, &c. and they are called Apodes, as eels; Jugulares, as cod; Thoracici, as perch; Abdominales, as pike and salmon.] LESSON 99. Structure and Transformation of Insects. Fa'cet a little face or side of a body cut into a number of angles. Lubricated, made smooth so as easily to glide over any part. Entomology, that branch of natural history which treats of insects. THE animals of this class are remarkable for a greater variety of powers and a more wonderful display of instinct and intelligence, than any other of the invertebral animals. They are distinguished by many peculiarities of form. Instead of a heart, insects have a vessel or reservoir situated along the back, extending from one end of their bodies to the other, and filled with a transparent fluid, which is supposed to answer the purpose of blood, and to be conveyed, by absorption, to the various organs. They have no parti 222 TRANSFORMATION OF INSECTS cular organ for respiration, but their bodies are penetrated in every direction by tubes, through which the air is trans mitted to every part. These tubes communicate externally by openings called spiracles. To serve the purpose of a brain and nervous system, they are furnished with two knotted cords running the length of their bodies. They possess the senses of seeing, tasting, smelling, and feeling; but organs of hearing, if they exist, have not yet been discovered. They are provided with a hard external covering which differs in different species; in some it forms a complete case of a horny or shell-like substance; and in others it consists merely in a tough muscular coat, divided into rings which surround the body. Their heads are furnished with anten'næ or feelers, which are a kind of filaments composed of joints, designed probably as the organs of the sense of touch, or of sensations still more delicate and of a nature totally unknown to us. The mouth of insects varies much in construction, according to the nature of their food. Some are armed with a sort of lancet, and others with a trunk or probos'cis, which in the butterflies is capable of being rolled up in a spiral form. Their eyes may be considered among the most surprising of nature's works. They differ much in form and colour in the different insects; but they are not, as might be at first supposed, mere hemispherical bodies of plane simple surfaces, for examination proves them to be composed of an immense assemblage of highly wrought hexagonal facets, each furnished with its proper optic nerve, retina, and other parts necessary for vision; the number of these facets differs in different species; eight thousand have been counted in the eye of the common fly, and twelve thousand in that of the dragon fly. How sweet to muse upon His skill displayed! TRANSFORMATION OF INSECTS. His mighty work who speaks, and it is done. 223 COWPER. Those which The greater part of insects are winged. are not winged, continue, during their whole existence, of the same form and structure as at birth. Those which are winged undergo certain changes of form, which are called their metamorphoses. They differ in number in different kinds of insects. For an example we may take the tribe of the Butterfly. From the egg of this insect is hatched an animal differing entirely from its parent. Its body is long and cylindrical, and divided into numerous rings. It is provided with a large number of very short legs, with jaws, and with several small eyes. It is familiarly known to us by the name of caterpillar. It lives in this state a considerable time, subsisting upon such food as is adapted to its nature. At length it casts off its skin, and appears in another form without limbs. It ceases to feed or to move. It seems to be totally without life. This is called the chrys'alis. After a while, by examining it closely, the imperfect shape of a butterfly may be distinguished through its surface; and finally the envelope is broken and the animal escapes. Its wings are at first short, weak, and moist, but they soon unfold to a greater size, and become strong; and the insect is in a state to fly. It has now six long legs, a spiral trunk, two antennæ, and eyes differing entirely from those of the caterpillar. In short, it is an animal totally different, delighting us by the beauty of its spots and the variety of its colours; and yet these wonderful changes are only the successive unfolding of parts contained one within another in the original em'bryo. In the first state the animal is called the larva; in the second the chrysalis or nympha; and the third is called the perfect state. A considerable portion of the insect tribes pass through these three changes of existence. But many only undergo what is called a demi-metamorphosis. Their larva resembles the perfect insect, except that it has no wings. And the only change they experience is, that in the nymph state they have the rudiments of wings, which finally on casting their skins, are changed into complete ones. - Such are grasshoppers and many others. When about to pass into the chrysalis state, which is a 224 TRANSFORMATION OF INSECTS. state of imbecility, insects select the most proper places and modes of concealing themselves from their enemies. Some, as the silk-worm and others, spin silken webs round their bodies, by which the animal form is completely disguised. Others leave the plants upon which they formerly fed, and hide themselves in little cells which they make in the earth. Some fix themselves by a gluten, and spin a rope round their middle to prevent them from falling. Others attach themselves to walls, with their heads higher than their bodies, but in various inclinations. In this state many remain motionless and seemingly inanimate, during the whole winter. Behold the insect race, ordained to keep ; QUESTIONS-1. For what are insects remarkable? 2. What have they instead of a heart? 3. What have they to answer the purpose of a respiratory organ? 4. Brain and nervous system? 5. What is said of their senses and external covering? 6. What are antennæ? 7. Describe the eyes of insects. 8. What are the changes called which winged insects undergo? 9. Give a description of these changes in the example of the butterfly. 10. What is the animal I called in its first-second-third state? 11. Describe what is called demi-metamorphosis. 12. What are some of the artifices of insects when about to enter the chrysalis state? [NOTE. All insects have six legs, with the exception of the millepedes, (pronounced millepēdz, or mil-lep'ē-dez) which have always more, and the number increases also with their age. Aurelia and Chrysalis are synonymous words, both alluding to the metallic or golden splendour of the case in which insects are enclosed during that state. This brilliancy however seems to be confined to the butterfly tribe. The name Pupa has lately been substituted for chrysalis and aurelia, because many insects in this state are thought to resemble an infant in swaddling clothes. |