PROFESSOR HUTTON ON ZOOLOGY

Otago Witness, Issue 1449, 30 August 1879, Page 17

PROFESSOR HUTTON ON ZOOLOGY

Professor Hutton delivered one of his courae of lectures on " Zoology," in the lecture-room of the Museum, Great King street, last Saturday afternoon. Although the weather was inclement, there was a very numerous audience, about 120 students being present. Th 9 subject of the lecture was " Vertebrate Animals." Professor Hutton said that vertebrate animals were distinguished from all the other subkingdoms they had been reviewing during the last few lectures by several marked peculiarities. So much was this the case that the animal kingdom used to be, and often now is, in a popular kind of way, divided into twodiviaionii—vertebrateand invertebrate animal*, The n ais point wbiob marked vertebrate animala

from invertebrate was not the possession of backbone or vertebra, but was in the general B J ructure of the body, vertebrate animals consisting of two tubes alongside one another, whereas in all invertebrate animals the body consisted of one tube. They would remember he had defined protozoa as animals consisting of cells or masses of protoplasm, with out any body cavity ; coelenterata, as in the lower grades, » body with a simple inner tube, and in the higher grades having a second tube hanging down into the inner tube, and vermes as having two tubes, one inside the other, the inside of one being the body cavity, and the inside of the other the alimentary canal. In vertebrate animals there was another advance, for in them they found two tubes running alongside one another, the back containing the nervous system. In the invertebrates also the nervous system — the ganglia — was found in the lower portion of the body, the same side a) the liinb*,-or what was called the mural side, and the heart, or circulatory system, was always f und on the side away from the limbs. In vertebrate animals exactly the opposite was the case ; the limbs coming from the side of the circulatory system, and the nervous system being found on tbe side furthest away from the limbs. The sympathetic system of the vertebrate animals was homologous with the nervous system of invertebrate animals, and therefore vertebrate animals had the same nervous system as invertebrates, and in addition to that the main nervous system, consisting of the spinal column and brains, which was in a separate tube from the body -tube of the animaL The mouth of invertebrate animals was found on the same side as the nervous system, and the consequence was that in all invetebrate animals the gullet traversed the nervous system, but in vertebrate animala this did not happen, the mouth being on the opposite sida to the nervous system. These were the points which really distinguished vertebrate from invertebrate animals. Of courae the possession of an internal bony skeleton was a point of great importance, but it was not fundamental, because there were some vertebrates without any bony skeleton. In the skeletons of a fish and a monkey (exhibited) they would notice a system of bones beginning at the head and running down to the tail. The skeletons consisted of a skull or braincap, the spinal column and its append, ages, and the axiel skeleton which carried four limbs, for no vertebrate animal had more than four limbs. The spinal column consisted of a number of vertebra. A vertebra was a solid piece of bone, from the top cf which two pieces of bone come up and unite together, forming a canal which covers the spinal cord, and from the sides of some of which ribs extended. The , .skull was a cavity which always had a large opening at its base or at its end — at its end in fishes, and at its base in mammalia— and through this opening the spinal column communicated with the biain. Next to the head came a number of cervical vertebrae ; then a number of vertebrae, each of which bore on its sides ribs ; then followed a number of lumbar vertebrae, which do not bear ribs ; then two or more vertebrae joined together into one bone ; and finally came the caudal or tail vertebrae. It was a common mistake to suppose that a bone was a dead part of an_ animal; the bone was as much a living part of an animal as its flesh ; it required nourishment and was supplied with blood, and iif cut would bleed from a* numerous pores, though not so freely as the'flash. Fishes formed the lowest division of vertebrated animals. The , first point which distinguished fishes was that ■ they breathed water by means of their gills during the whole of their lives. The means by which respiration was carried on and the circulatory system in fishes were comparatively simple. The heart of a fish consisted only of two chambers — an auricle and a ventricle. The auricle received the blood from all parts of the body, from it passes into tbe ventricle, from which it was driven to the gills, the respiratory organs, and thence passed throughout the body to the heartagain. Other pointsof distinction were tbat fishes' limbs were modified into fins ; that they had no neck, the head being joined on to the vertebras-carrying ribs ; and that there was no difference between the lumbar vertebrae and the caudal vertebrae ; in fact, the tail began • where the ribs stopped, and what was popularly regarded as the fish's tail was only the tail-fin. In the fish the tail-fin was always vertical ; but in the mammalia-rthe porpoise, whale, &c. — which looked like, but were not fishes, the tail was always horizontal, Amphibians'were distinguished from fish by the fact that although in an immature state they breathed by broncbia, or gills, in the adult state they breathed by lungs; but the difference between some amphibia and some fish was very small — in fact, the two claeses run together, but generally id was considered that the absence of fins distinguished the amphibian from the fish if it had the other characteristics. The amphibians were divided into two very distinct orders — one of which had a tail all its life, while the other lost its tail when it grew old ; the latter class were known by tbe names of Irogs and toads, which began life as tadpoles, and the former were represented by newts. The next class cf vertebrated animals were reptiles, which never respired water during any period of their existence, and were distinguished by a peculiarity (also found in birds) that the first two vertebrae next the head are more or less modified, %o as to fit the vertebral column to ona cavity in the skull. Iv the reptile the circulatory system differed from that of the fishes ; the heart consisting of three chambers — a ventrioal and two auricles, and the process of circulation being that the blood from different parts of the body entered one of the auricle 3, was forcsd by this auricle into the ventricle, from which it was driven in two directions — part .g the lungs and part to the different organs of the body — so that the ventric of the heart contained blood only partially purified. Reptileß were also generally covered with scales, whereas amphibians had a soft akin, never covered with scales. Snakes formed one division of reptiles — they were animals without legs, and remarkable fir the size of their jaws, which were so constructed that it could swallow another animal larger than itself. The divisions of reptiles which comprised tortoises and turtles was the most extraordinary. In the tortoise and turtle the ribß grew out into a bony process, which joined together, forming a complete covering to the animaL The great peculiarity, however, was tbat the shouldergirdle and the leg-girdle grew inside the body cavity ef the tortoise and turtle ; but when young their • limbs were found in the ordinary form, and it was only by the process of growth that the order was reversed. Birds were a class readily distinguished from all others. The principal points to be noticed in the skeleton of a bird was that its fore-limbs were developed into wings, tbat the bones were peculiarly modified, and that its breast-bone was enormously developed. The skull and backbone, and ths structure of tho limbs of birds and reptiles were, however, very similar, and there were intermediate forma which closely connected them ; but the circulatory system of the bird was far superior to that of the reptile. Strictly speaking, it was on the reptilian type, but bo modified as to be very similar to the mammalian type, The heart in the bird, as in mammals, consisted of four chambers'—two /wiricles «ftO tiro ventriclw, or, m it vrtre,

two hearts joined together, one of which received tbe impure blood from the body and drove it to the lunga, and the other received^ the purified blood from the lungs snd drove ib to the body. The heat of the blood depended upon the respiration of the animals, and the tsrm cold-blooded, applied to fishes and reptiles, wai only a relative term. The highest of all divisions was the mammalian — distinguished by the head being joined to th-s vertebral column by means of two articulations^ ; by the body being generally covered with hair instead of feathers or scales ; and by the fact that the young, after birth, depend directly upon^ the parents for nourishment. The first division was very important to residents in Australasia, as in Australia alone the class was found. Ib consisted of two animal? only — the platypus or duckbill, and an animal called the porcupine ant-eater, though it was meither a porcupine nor an ant-eater. The second division consisted of marsupial animals ; and all other mammalia were included in the third division. Man differed very little from other mammals so far as bodily structure was concerned, his distinguishing point being his mental attainments. If a naturalist had to classify man sincplyby his internal structure, he would be obliged to place him amongst other animals, only in a distinct family. Professor Hutton announced at the conclusion of the lecture, that the last lecture of the course would be given on Saturday next — subject : "The Geographical Distribution of Animals."