CHORDATA

CHORDATA

Class: Reptilia

Distinction between a poisonous and non-poisonous snake

A poisonous snake has poison apparatus consisting of poison gland, poison duct and poisonous teeth called fangs. Poisonous gland lies behind the eyes and the duct runs from it upto the base of the fang. The fang contains a groove or a tunnel which opens at the tip of the fang.

Identification on the basis of bite

(i) If two large holes are present at the site of bite surrounded by lateral rows of small holes-poisonous.

(ii) Large holes absent but small lateral holes are present-non poisonous.

Identification on the basis of external characters

To know whether a snake is poisonous or not the tail should be examined first.

(i) If the tail is flat and head is covered by large shields then it is a sea-snake. All sea snakes are poisonous except Distira cyanocincta whose head is covered by small scales.

(ii) If the tail is cylindrical the snake may be poisonous or non poisonous. Next examine the belly.

Ventral scales on belly

A. If the belly is covered by small scales the snake is non-poisonous.

B. If the belly is covered laterally by small scales and median ventral scales are transverse but do not reach the lateral sides, the snake is non-poisonous. It is Python.

C. If the belly is completely covered by large transverse scales then the snake may be poisonous or non-poisonous. To know the poisonous snakes examine the head.

1. If the head is covered by small scales on its dorsal surface, the snake is poisonous. It is a viper, Vipera

2. If the head is covered by large scales the snake is poisonous or non-poisonous. Then look for the following charactes.

(a) If a pit is present between eye and nostril in the given snake and the head is partially covered by small scales it is poisonous. It is pit-viper, Angkistrodon.

(b) If a pit is absent and 3^rd supra-labial scales is largest and touches eye and nasal then the snake is poisonous. It is cobra or king-cobra. It has also to rows of sub-caudals on the ventral surface of tail.

(c) If (a) and (b) are absent but the 4^th infra-labial is largest, back is with mid-dorsal row of large hexagonal scales or vertebral and one row of sub-caudals on the ventral surface of tail then the snake is poisonous. It is a Krait, Bungaras

(d) If head is covered by large shields but pit is absent, rd supra-labial does not touch eye and nasal, 4^th infra-labial is not largest and there is no hexagonal scales on mid dorsal region then the snake is non-poisonous. It may be rat snake, water snake etc.

Mammalia

Mammalia

Rabbit, Hare and Guinea-pig

The common rabbit and hare were previously included in the same genus Lepus but W. N. Parker placed these under two separate genera on the basis of the structure of caecum. Rabbit belongs to genus Oryctologus and here to Lepus.

The common here, Lepus Europeans is found throughout Europe except northern Russia.

Another species Lepus timidus is found in Ireland, some part of Europe and sometimes also in Japan. Lepus americanus is found in America. Lepus crawshayi and Lepus whytei both are found in Africa.

Oryctolagus was first found in Western Europe and Africa. Dispersal of this animal to different parts of the world took place by human agency. Domesticated rabbit is found in many places of India. By inter and cross breeding various varieties of rabbit have been produced. Some of these are white, some are black or spotted.

Cavia procellus (guinea-pig) is a kind of herbivorous terrestrial mammal which assembles rabbit. This is generally used in various laboratories of India for study purposes. Cavia is a small mammal found throughout India. It differs from rabbit in the following characters-

(i) Neck is smaller than rabbit

(ii) Pinna is smaller

(iii) Eye lashes are absent

(iv) Tail is absent, represented by only a small root.

(v) Fore-limb with four and hind-limb with three clawed digits.

CLASSIFICATION

Phylum-Chordata

Group-Craniata (vertebrata)

Division-Gnathostomata

Super-class-Tetrapoda

Class-Mammalia

Sub-class-Theria

Order-Logomorpha

Genus-Oryctolagus

Species-O. cuniculus

Evolution of Man

Evolution of Man

The first arboreal, shrew-like insectivorous animals gave rise to Primates, an order of class mammalia. In this order man belongs. Fossil history shows that primates evolved during Paleocene. From early prosimians or first primates five groups of animals radiated. These were –

(i) Lemuroids – Lemurs (long snout) of Madagascar island.

(ii) Tarsoids –Tarsier (short neck) of southern Asia and lndonesia.

(iii) Ceboids- New world monkeys with prehensile tail of South and Central America.

(iv) Carcopithecoids-Old world monkeys with non-prehensile tail Africa and Asia.

(v) Hominoids –Represented by apes and man. During early Miocene period hominoid gave rise to two branches –one formed pongids or apes (i.e. gibbons, orangutans, chimpanzees and gorillas) and the other gave rise to hominids to which man belongs.

There are some similarities between apes and man. There are (i) absence of tail; (ii) legs are long; (iii) broad sternum leading to broad and flat breast; (iv) 4 or 5 lumbar vertebrae; (v) brain and cranial cavity large; (vi) omnivorous nutrition and development of domestic life. But these two also differ in some characters. These are (i) apes are arboreal while man is terrestrial; (ii) apes are with thick hairs all over the body while man has lesser hairs on limited regions of the body;(iii) apes have upper lip without median furrow but this is present in man;(iv) well developed mammary glands in females but not so in apes;(v) separate pre-maxilla and maxilla in apes but in man these are fused;(vi) ‘U’ shaped dental line in ape but semicircular in man;(vii) incisors and canines a little larger than other teeth in ape but in man these are almost of the same length like other teeth;(viii) in ape foramen magnum at the posterior end of skull which lies in front of vertebral column but in man the skull lies anterior to vertebral column; (ix) power of speech and imagination lacking in apes but present in man;(x) brain and cranial cavity is comparatively smaller in apes than in man.

1. Pre-Apes

During the study of fossil history of man scientists came across many fossils of pre-apes. The important among them are –

1. Propliopithecus and Pliopithecus – These are fossils of Oligocene period which resemble more with ape and man than monkey. These are considered to be the stage from where the evolutionary-series of ape and man started.

2. Limnopithecus and Pliopithecus –These are fossils of miocenc and Pliocene period. These are considered as members of a branch which separated from evolutionary line of apes an

man and became extinct afterwards.

3. Procunsul –During Miocene period ape and monkey were undergoing evolutionary changes in Africa and India. During this time a famous fossils was discovered which is named as Procunsul Africana. Incomplete skeleton of Procunsul was discovered in Victoria lake, Africa during 1948 by Dr. Leake. In some characters it stands between ape and man. The skull was round like man but long canine was like ape.

Scientists believe that Procunsul was at such a evolutionary step from where preman and ancestors of pre-ape (primates) diverged but was not in the direct line of the evolution of man. This skeleton was 2crore50lac of years old.

4. Dryopithecus –The fossil of this pre-ape was obtained from middle Miocene and early Pliocene strata of Europe and Africa.

5. Shivapithecus –It was another pre-ape whose fossil was discovered from Miocene strata of Siwalik hill of India. Its skull and hands were like monkey but jaw with teeth was ape-like. From this stage ancestors of man and ape separated.

On the basis of the accumulated evidences it is very difficult to say when man evolved. Human evolutionary changes are the following –

(i) Erect posture (ii) shortening of arms (iii) reduction in size of teeth (iv) loss of jaw power (v) increase in skull capacity (vi)reduction of brow ridges (vii)power of articulated speech (viii)utilization of tools and weapons. The present fossils indicate that man has originated from ancestor man-like ape in Africa. Skeleton and experiments associated with serum show that man had closer relation with man-like gorilla, chimpanzee etc. So we can accept that man and man-like ape descended from some common ancestor.

2. Pre historic Man

During evolution of man, there appeared several races which existed for sometimes and then became extinct. These are called pre-historic man.

(A) Pre-hominid Ancestors(man ape)

(a) Ramapithecus and Kenyapithecus- Fossils of these prehominid were found in Siwalik hills of N-W India by G.E.Lewis(1930) and during Miocene and Pliocene strata of Africa and China by L.S.B.Leakey (1955). These were prehomonid ancestors because these had-

(i) semicu

EVOLUTION

EVOLUTION

If we look around we see many kinds of plants and animals. They differ from each other in different characters. When one studies about plants and animals the first question that arises in his mind is about origin and evolution of these plants and animals on earth. How they originated? When they originated? How they evolved and give rise to the diversified animals? Whether God has created them as such or they have changed slowly during their life in different lines and now exist as such? From ancient times scientists are trying to solve these questions. The most important question before them was how life originated and how they evolved? We now know that life originated in water. These are considered as simple and lower plants and animals. These then invaded the land and changed according to the surrounding to live in the changed atmosphere. This change was slow and ultimately gave rise to complex and higher plants and animals. So we can define evolution as a slow and progressive change resulting in increasing complexity of living simple and lower plants and animals which has taken place during millions of years to give rise to different complex and higher plants and animals on this earth.

Endocrine Glands

Endocrine Glands

Hormones are chemical substance which are required in minute quantity for the normal functioning of the body. Both plants and animals secrete hormones of different kinds to control different physiological body functions. In the absence of particular hormones some disorder take place in body functions.

Hormones were first designated as ‘Secretin’ by Bayliss and Starling (1902) and the word hormones was first used by Starling (1906) for certain chemical substances secreted by animals. In animals these chemical substance are secreted by endocrine glands and carried by blood to different parts of the body where they control and regulate the normal physiological functions of the body. The word ‘endocrine’ is a Greek word which means internal secretion Endocrine glands have no ducts, so they are also called ductless glands. As hormones are secreted within the body they are called internal secretions. Hormones are chemical substances and control the body functions so they are called chemical messengers or chemical co-ordinators. Some hormones are made of steroids, some are made of amino acids or proteins. Many of them have been synthesized in the laboratory.

EMBRYOLOGY

EMBRYOLOGY

Embryology (Gr. Embryon= mbryo ; logos = discourse) is the science which deals with the development of an organism. Development is the series of change that take place in a Zygote (fertilized egg) or bud (formed in asexual reproduction) to form a complete organism. Development can be divided into two phases-

(i) Pre-natal or embryonic development. This development which takes place within the egg or womb of the mother upto birth. The study of the changes taking place during this period is also called embryology.

(ii) Post-natal or post-embryonic development. This period is the development from the birth of the organism up to death of the organism.

Ontology is the entire development of the fertilized egg (e.g. life-cycle) whereas phylogeny is the ancestral or revolutionary history of species of higher groups.

ANIMAL CELL

ANIMAL CELL

Cytology is the branch of biology which deals with the structures of cell and its organelles and their functions. Cell is made of protoplasm which is surrounded by cell membrane and contains a nucleus. Cell is generally defined as “Cell is the structural and functional unit of living organisms” or “Cell is the unit of life”.

History

The study of cell was possible by the discovery of microscope by two scientists named Z. Janssen and H. Janssen in 1590. The word cell is associated with the name of Robert Hooke. In 1665 he observed under the microscope small spaces surrounded by the walls in a thin section of cork. This looked like honey comb. He called these spaces as cells (lat. Cell=Hollow space) which mean hollow space. In 1674 A. Van Leeuwenhoek (1632-1723) improved the lens system of this microscope by grinding and was the first to observe bacteria. He also observed various protozoan, sperms, erythrocytes (RBC) etc. in 1759 K. F. Wolf (1733-94) started that cells are found in living substances.

In 1805 Lorenz Oken (1779-1851) said that every organic being originated and is made of cells. In 1824 French scientist R. J. H. Detrochet observed that each plant and animal tissue is formed by different kinds of cells. In 1831 Robert Brown discovered the nucleus and showed that it is present in all Cells.

The famous German botanist M. J. Schleiden in 1838 stated that the body of a plant is made of microscopic cells and each cell is the unit of plant. Another German Zoologist T. S. Schwann observed in 1839 that animal body is also made of cells. Combining these two views Schwann and Schleiden (1838-39) formulated the famous Cell theory. According to this theory-

(i) All living organisms are made up of cells.

(ii) Every organism originated from a cell.

(iii) Each cell is an independent unit, yet they function together resulting in an organism.

(iv) Cells originated by a process of building in which the nucleus plays the part of creater

In 1839 J. E. Purkinje and in 1846 Hugo Von Mohl proposed the name Protoplasm for the living substance present in a cell. After this study of cell progressed with the help of better microscopes and use of chemical and physical techniques of investigation .In 1875 Van Beneden observed the centrioles, in 1879 W. Fleming reported the chromatin of the nucleus and used the term mitosis for cell division in 1882. He was the first to observe mitochondria but called them bioplast in 1894. In 1897 Altmann and C. Benda named these as mitochondria. In the nerve cells of barn owl Comillo Golgi first observed the Golgi apparatus in 1898. The term chromo some was coined by Waldeyer (1888). Wilson (1900) first described the structure of a typical cell. Then M. Knoll and E. Ruska (1932) invented the electron microscope which helped us to know in great detail about plasma membrane, mitochondria, endoplasmic reticulum, ribosome, lysosome, pinocyte etc.