Natural History.

Otago Witness, Issue 1488, 22 May 1880, Page 27

Natural History.

NOTES FOR THS YOUJSG.-THE VERTiSBRATA.

By Uncle David.

All the animals which we have glanced at this year from the sponge {protoza) up to the shellfish {mollusca) are usually grouped together under the name of Invertebrata, which means invertebrate animals, or animals which have no backbone. This backbone is also called the spine or vertebral column, hence the name invertebrata—having no vertebral column. The only subkingdom which we have now to consider is the vertebrata, or animals having a backbone, But before I describe any of the individuals of this great subkingdom, I will notice briefly tho chief characteristics of the Bubkingdom itaelf. The first grand character, then, which distinguishes the veretebrate animals is the possession of an internal bony skeleton, which is indued with life, nourished by bloodvessels, and which is capable of growth. In the lowest classes of the vertebrata the internal framework of the body never reaches a bony state, but remains throughout life in a state of gristle. When, however, greater strength is required for more active and forcible moveiaenfco, earthy particles enter into the composition of the gristly framework, additional firmness is imparted to it, and the skeleton becomes at length converted into perfect bon». The skeleton of a vertebrate animal is composed of several sets of bone?, some of which are employed for vory different purposes. There is one part of the skeleton which we fiad in almost if not quite every member of the sub-king-dom, and that is the backbone, which formß, as it were, the main line and centre of the whole bony framework. To the backbone we find jointed four limbs— never more than four, though in some members we fiad only two — as in the mud eela which are found plentifully in ths rice fields of Carolina. These animals are very like the oommon eal in general shape, but instead of fins they have two very short and feeble legs. In other members again we find no limbs at all, as in the sea-serpents and snakes. Another feature of the vertebrata is the greater development of the nervous system. This system consists of the brain, contained within the hollow of the skull, and continued from which is the spinal marrow or spinal cord, lodged in a tube formed by tho backbone. From the Bpinal cord there run out nerves in regular pairs, which again send out multitudes of smaller nerves to every part of the body. "The nervous system may thus be compared to an electric telegraph, of which the brain is the central office, and the nerves the wires, along which travel with inconceivable rapidity the various commands and reports from all parts of the complex system." In consequence of the increased development of the nervous system we find a greater development of the organs of the senses, especially those of hearing, taste, and smell ; and thus with iuoreased intelligence the vertebrates have higher capabilities of enjoyment. Again the blood of all the vertebrates is red, and it contains myriads of minute bodies called globules or corpuscles. These corpuscles do not always present the same form or size; those found in the human blood are circular in form, and are only about one three thousand five hundreths of an inch in diameter. In the ciass of fishes, owing to the imperfect ci>ndil.icm of the breathing apparatus, the lioat of the body is scarcely higher than that of the water which surrounds it ; and even in reptiles such is the sluggish condition of the circulation of the blood, that the standard of heat in them is still very low ; but in the higher classes, the birds and

mammals, the circulation is muoh more rapid. The warmth of the body is consequently increased, and these animals are constantly kept at a higher temperature than tbat of tbe air or water iv which they live. Hence the distinction generally mwie between the hot-blooded and the cold-blooded animals. Now in order to retain a higher degtee of animal heat the animal must have a waTm and thick covering of some non-conducting material, consequently, in the hair, wool, and feathers of the warm blooded tribes, we at once see the provision made by Nature for preventing an unnecessary expenditure of that heat which is so needful for their wellbeing. Such coverings would be more than useless to the inhabitants of a watery element, and so in fishes, which are destined to a watery life, wo tiud no such incumbrcnees, but in their place a scaly or slippery covering more fitted to their habits, and in aocordance too with the lower temperature of their blood. The incr«ased heat of the blood has a most wonderful effect upon the instincts and affections of tiae different races of the vertebrata. The cold blooded fisheß have^no affection for their young; they cast their spawn upon the water and go away quite regardless of the young offspring to bo derived from it. The chilly reptile, also destitute of maternal affection, is quite content to I* ave her effgs to the hatching influence of the sun until the young escape. But no I sooner does the animal heat become sufficient than all the sympathies of parental love appear ; and the bird, as she patiently performs the bußines? of hatching or tenderly watches over hdr young brood, derives a pleasure which is almost as great as that enjoyed by the mother, who from her own breast supplies the nourishment prepared by Nature for the support of her darliug iittle