Euglena
       
                   Phylum            : Protozoa-Unicellular organisms.
                  Sub-phylum      : Sarcomastigophora-Locomotion by pseudopodia or flagella.
                  Class                 : Matigophora- Locomotion by flagella; body enclosed in a pellicle.
                  Sub-class           : Phytomastigina-Nutrition holophytic; possess chromatophores.
                  Order                 : Euglenoidea-cytosome and cytopharynx present; flagellum single.
                  Genus                : Euglena.


Habit and Habitat

Euglena is cosmopolitan in distribution and occurs in all stagnant fresh water ponds, pools and ditches containing decaying animal and vegetable matter. in the laboratory, it can be culture by placing a few Euglena in the culture medium prepared by boiling horse or cow dung in distilled water.

Structure 

The animal body is spindle-shaped with a blunt anterior end, and a pointed posterior end. The outer covering , known as pellicle is firm and elastic and thus it gives a fixed shape to the animal. Beneath the pellicle, there are a few elastic fibers arranged obliquely and longitudinally.
                                                                                                                The anterior end beare a funnel-like cytosome which leads into a short Cytopharynx. Near the base of the cytostome, there is a large pigment spot, known as stigma.
         From the base of the cytostome arises a large flagellum which has two roots, joining with the basal grannule (blepharoplast) . Besides, a short filament also arises with a separate basal grannule, which soon after its origin unites with the anger one.
         The cytoplasm is well differentiated into an outer thin, non-granular ectoplasm and an inner grannule, vacuolated endoplasm. In the endoplasm, there is a large, spherical nucleus situated almost centrally. Several chloroplast and amylum bodies occur suspended in the endoplasm. One to many contractile vaculoes are met at the anterior end and in close proximation with the cytopharynx.


Locomotion

Euglena shows two type of movements, viz (a) flagellar movements, and (b) euglenoid movements.

(a)  Flagellar movements. They take place by lashing movement of flagellum in the water. The long highly contractile flagellum creates a series of waves of motion. This helps in propeling the body forward with a spiral rotation along the axis. This is the cheif means of locomotion in Euglena.

(b) Euglenoid movements. The body covering (or pellicle) is flexible and elastic in Euglena. It can change its shape according to the requirements of the animal. In this process, a wave of contractile pass along the body from anterior end and the animal creeps forward. The body becomes shorter and widen first at the posterior end. The oeganism thus progresses
slowly. These movements are caused by the stretching of protoplasm on the pellicle or by the action of myonemes of the ectoplasm. This type of movement is occasional.

Nutrition

Euglena show mixotrophic type of nutrition, as it exhibits more than one type of feeding. Commonly three types of nutrition viz. Holozoic, Holophytic and Saprophytic are met in Euglena.

1. Holozoic. The holozoic nutrition is rare in Eyglena. In the process, the animal takes in the living solid food particles and digest them.

2. Holophytic. During holophytic nutrition, Euglena is able to prepare its own food by photosynthesis. As a result paramylum is formed. The holophytic nutrition occurs in the presence of sun-light and the green pigment chlorophyll play an importantrole in the process.

3. Saprophytic. In poor light or darkness, Euglena exhibits saprophytic mode of nutrition. Dead and decaying matters dissolved in pond water are digested extracellularly and absorbed through the general body surface.

Respiration

It is simple and aerobic, Gaseous exchange take place by diffusion through general body surface.The dissolved oxygen of the surrounding water it taken in and carbon dioxide of the body passes out in a similar way.

Excretion and Osmoregulation 

The cytostome, reservoir and contractile vacuoles are concerned with the excretion and osmoregulation.The tributary canals collect excess water and waste nitrogenous products from the cytoplasm and pour them in the contractile vacuole. The vacuoles diffuse into the reservoir from where water goes outside through cytopharynx and cytostome. Excretory wastes are also diffused through general body.

Reproduction

Euglena does not reproduce sexually. The usual mode of reproduction is by longitudinal binary fission also occur.

(a)  Binary fission. This type of reproduction is very common in Euglena. When the environment conditions are favourable for growth, the animal ceases its activites and secretes a mucilaginous envelope around itself. The nucleus divides by simple mitosis. Other nuclear and extra-nuclear inclusions starts from the anterior end of the body. However the flagellum does not divide and goes for one individual while the other develops its own. The two daughter euglenae thus fromed lead a new life.

(b) Encystment and Multiple fission. During unfavourable condition, Euglena reproduces either by encystment or by multiple fission. During encystment, if secretes thick cyst of gelatinous mass of yellowish brown colour. It can withstand the adverse conditions of life. Onset of fevourable conditions result in the rupture of cyst and the animal starts an active life.

        In multiple fission, during the encystment it may undergo several longitudinal binary fission. All of them remain entangled in a common cyst forming the palmella stage. When favourable  condition commence, the cyst wall ruptures, the euglenae separate, regenerate the flagella and starts living normal and active life.

Systematic Position of Euglena 

Euglena bears many characters which are common to both plants and animal. The botanists kept it in plant kingdom due to the presence of chloroplast, pyrenoids and holophytic mode of nutrition. However, the characters like the presence of myonemes, contractile vacuoles and euglenoid type of movement compel us to keep it in the animal kingdom. Furthermore, absence of a cellulose cell wall, the presence of paramylum and holozoic mode of nutrition strengthens this view. In animal kingdom, we treat it as member of phylum Protozoa due to its unicellular microscopic body and we include it in class Mastigophora bacause  it has a flagellum for the movements.

Cytogamy

It has been reported in P. caudatum. It is an intermdiate process between conjugation and autogamy. In this process, two individuals come together for some time. Their nuclei undergo changes as occurring during conjugation, i.e. unicronucleus divides twice to form four daughter nuclei, the first division being meiotic one. Out of the four nuclei, three degenerate and the remaining one of each conjugant divides to form two nuclei. Both the nuclei fuse together in the protoplasmic cone to form a synkaryon. Thus, in this process, nuclear exchange like that of conjugation does not take place. The individuals than separate and divide.


Autogamy

Autogamy is a type of reorganisation  found in P. aurelia. It is a sort of conjugation process in which only one organism takes part. During this process, the two micronuclei of the same individual fuse together forming a synkaron. During the process, macronucleus degenerate. Both the micronuclei divide thrice into a number of daughter nuclei. The first division is being the meiotic one. Thereafter, all the nuclei degenerate except two which fuse together to form s synkayon in a protoplasmic cone. The synkaryon divide to produce four daughter nuclei; out of the four two differentiate as macro and two as micronuclei. The cell body divides by a transverse construction and the micronuclei divide simultaneously two daughter paramecia.

Encystment

This phenomenon has been reported only in P. bursaria. During unfavoutable condition the body of paramecium become oval and it secretes a thick cyst round itself to yide over the unfavourable condition. The cyst appear like sand grains.

Nuclear reorganisation 

Degeneration of old macronucleus and formation of a new one by the fusion of micronuclei is called nuclear organisation. During binary fission, the macronucleus  divides by anitosis in which chromosomes are distributed at random in the daughter macronuclei. The genic balance of macronucleus is disturbed due to repreated binary fission. This results in less vigour and vitality of the daughter individuals. After passing through a certain number of asexual generations, the daughter paramecia die for want of nuclear reorganisation. Replacement of such a macronucleus becomes necessary to rejuvenate the aging paramecia. This old and decaying macronucleus is replaced by a new one during conjugation, endomixis.

Conjugation 

It is the temoorary pairing of two individual of the same species but of two different mating types. In this process, two individuals come together and attach themselves by their ventral surface. These two individual are called as conjugation. Before entering into actual process, they become sluggish. At the point of contact, the pellicle is dissolved and the cytoplasm of both the conjugant becomes continuous. In the process, the macronucleus degenerate and the micronucleus divides twice to form four micronuclei; out of the four micronuclei, three degenerate and the remaining one divides unequally to form a large female nuclei and a small male nuclei. The migratory nuclei of both the conjugation are exchanged so that the male nuclei of one passes into the other and fuses with the zygote nucleus (synkaryon). Thereafter, both the conjugation get separated and are called as exconjugants. The synkaryon nucleus divides successively into two, four and eight nuclei. Out of the eight nuclei, four become the macronucleus and three out of the remaining four degenerate and the remaining one acts as micronucleus. Now each exconjugant divides  in to two by transverse fission to form four paramecia, each having a single micronuclei and a macronuclei. Each daughter paramecia may divide further to form eight daughter paramecia.
female nuclei forming the

Signification. Conjugation is an important phenomenon in the life of Paramecium. It serves as a process of rejuvenation and reorganisation by which the vitality is restored. It combines the genetic material of two individuals of different mating types that resultsin increased vigour of the offspring.

ENDOMIXIS   IN   PARAMECIUM

It occurs in P. aurellia which has two micronuclei and one macronucleus. During the process of endomixis, macronucleus disappear by by degeneration, and the micronuclei divide twice to form eight micronuclei. A transverse constriction, horizonal to the longitudinal body axis divides the animal into two each having four daughter micronuclei. In each half, three micronuclei degenerate, and the remaining micronuclei of each daughter cell divides twice to form four nuclei, two of which become the micronuclei and two macronuclei. The remaining two micronuclei again divide automatically resulting into four micronuclei. Now each cell again divides, each daughter individual has now one macro and two micronuclei. New contractile vacuoles and ingestatory  apparatus develop in each daughter paramecia. Thus, from one organism, four daughter paramecia are formed.
               Endomixis is of high significance. It is actually the phenomenon of nuclear reorganisation followed by the division of body with in a singal individual, with no nuclear exchange or fusion. As a result of endomixis, four daughter paramecia are formed from a singal parent, thus it is a mode of multiplication. It serves as a substitute for conjugation as reorganization and readjustment of the nuclear material and cytoplasm during endomixis result in to rejuvenescence.






                                                                                                                                      Paramecium, stages in endomixis.


HEMIXIS 
It is a simple phenomenon of nuclear reorganisation found in P. aurellia. In the process, the micronuclei remain inert and the meganucleus separate off several minute chromatin part which are abscribed in the surrounding of cytoplasm. The micro and meganuclei then behave normally and divide by usual manner. Hemixis is believed to be an act by which the macronucleus is purified.











                                                                                                                                                                             Paramecium, stage in hemixis.

EXCRETION

Waste product are diffused through general body surface, egested through cytopyge and by contractile vacuoles.

Respiration. It take place through general body surface. Gaseous exchange takes place by diffusion; oxygen is taken in form the surrounding water and carbon dioxide is diffused in water.

Osmoregulation. Water control (osmoregulation) is regulated by two contractile vacuoles. Each contractile vacuole is provided with 6-11 radiating canals which go deep into the endoplasm and collect excess of water. The water from the canal is stored in the contractile vacuoles from where it is discharged to the out side through temporary structure.

REPRODUCTION     IN     PARAMECIUM

Paramecium reproduces both by asexual and sexual means.

A. Asexual reproduction. It takes place generally by binary fission. In some species like P. aurelia endomixis and hemixis also take place.

B. Sexual reproduction. During favourable condition, it take place by conjugation. In some species autotomy, cytogamy or encystment also occur.

BINARY  FISSION   IN   PARAMECIUM

Under favourable survival conditions, it reproduces by binary fission . During this process, the animal body becomes flat and spindle shaped. The activities like locomotion, nutrition, etc. cease and animal settles down at the bottom of water. During this type of reproduction the animal divides transversely into two unequal halves. The micronucleus elongated and undergoes a sort of mitosis while the macronucleus elongated and divides transversely into two parts automatically. The cleavage starts near the middle of the body. This deepens  and finally the two individuals are separated. The buccal groove goes to one half while the other develops its own. New contractile vacuoles are formed in each daughter colony.                                                                                                                                                            Paramecium, stages in binary fission.

LOCOMOTION
Paramecium exhibits two type of movement, viz.(a) creeping movements, and (b) swimming movements.

(a) creeping movements. During creeping movements, Paramecium uses its cilia of the oral surface for movements and simply glides over the substratum. As the pellicle is thin and elastic, it can easily bend and move from one place to another. It can squeeze itself through a space narrower than itself, after which the body assumes its normal shape.

(b) Swimming movements. The animal can swim forwards and backwards, This type of movement is performed by fin hair-like protoplasmic processes covering the entire animal. The beating of cilia is controlled by the neuro motor apparatus. During locomotion, cilia first bend like a bow with a slight spiral twist, then they straighten out again. Waves of contraction and bending of cilia pass from one end to the other. This coordinated movement of cilia is called metachronal rhythm which brings about forward and backward locomotion. The animal swims in an elongated spiral path and the individual body rotates upon its own longitudinal axis.

NUTRITION  IN PARAMECIUM AND CYCLOSIS

Paramecium is a holozoic in nutrition. It feeds upon bacteria, minute protozoa and organic detritus. The cilia lining the oral groove perform a great role in capturing food particles. During ingestion, the animal move in the direction of food. The cilia present on the peristomial groove beat in such a manner to withdraw food particles in to the peristomial groove. The food particle are collected at the bottom of the gullet and are concentrated into a ball in the endoplasm. These pass through the cytosome to form food vacuoles in the endoplasm, As soon as one food vacuoles detaches form the gullet, anotherone start forming. In the endoplasm, food vacuoles move on a fixed route due to definite streaming movement of the cytoplasm, known as cyclosis. The food vacuoles first travel to the posterior end then take a turn and travel anteriorly, then they pass downwards towards the cytoptge. The food vacuoles undergo changes in size and appearance of the contained food. The endoplasm secretes some enzymes into the food vacuoles which help in the digestion of carbohydrates and proteins. At first digestion occurs in an acidic medium, but later the contents of vacuoles become alkaline. Paramecium cannot digest fats. The undigested food is eliminated from the body through a definite present on the ventral surface posterior to the mouth.