Lets know about Homologous analogous and vestigial organs

Homologus organs

Homol­o­gy is a sim­i­lar­i­ty of struc­ture in var­i­ous organ­isms aris­ing from com­mon ances­try and is usu­al­ly reflect­ed in com­mon embry­olog­i­cal origin.Such struc­tures called homo­lo­gus organs are the con­se­quences of diver­gent evo­lu­tion and enable the organ­ism to car­ried out dif­fer­ent functions.

Super­fi­cial­ly, they look dif­fer­ent. the study of homolo­gies is a major aspect of com­par­a­tive anato­my. exam­ple of homolo­gies in organs and organ sys­tem of all groups of liv­ing organisms.

These homo­logues pro­vide impor­tant evi­dence for evo­lu­tion. the fore­limbs of ver­te­brates pro­vide an excel­lent exam­ple of organ with sim­i­lar struc­ture but dif­fer­ent func­tion. The fol­low­ing of sev­er­al ver­te­brates such as those of amphib­ians, Lizards, Birds, bats and men are all con­struct­ed on the same base plan and include sim­i­lar bone in the same position.

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Amphib­ians

But they have become mor­pho­log­i­cal­ly dif­fer­ent in the course of evo­lu­tion as a result of mod­i­fi­ca­tion to suit dif­fer­ent require­ments. Some exam­ples of ver­te­brate fore­limbs mod­i­fied to suit var­i­ous functions.

A spe­cial type of homol­o­gy is shown by metamer­ic ani­mals. A strik­ing exam­ple is that of the appendages of arthro­pods espe­cial­ly those of crustaceans.In the typ­i­cal crus­tacean pair of appendages is borne by each seg­ment of the body. it is appendages have evolved from a sin­gle struc­ture plan and mod­i­fy in a ser­i­al order so as to per­form var­i­ous func­tion this is known as ser­i­al Homol­o­gy. An Exam­ple of ser­i­al homol­o­gy in the prawn.

Homol­o­gy Rep­re­sent the con­se­quence of adap­tive radi­a­tion from a com­mon ances­tor in every organ­ism to adapt to dif­fer­ent eco­log­i­cal niches.

Clas­si­cal exam­ple of adap­tive radi­a­tion is a struc­ture of the fol­low­ing of mam­mals .there is always a sin­gle long bone the humerus in the upper arm.In the forum there are two par­al­lel bones the Anna and the radius in the wrist they are typ­i­cal­ly 8 carpal bones are arranged as two rows of four.5 par­al­lel metacarpals from The Skele­ton of the palm of the hand and row of three pha­langes each from skele­ton of the dig­it expect­ing the first dig­it which has only two phalanges.

The ten­recs (scaly ant eater) of the order insec­tivo­ra show the prim­i­tive pen­tadactyl and structure.The moles, which are at rel­a­tives are high­ly mod­i­fied for dig­ging in order to adapt a sub­ter­ranean habitat.

All the bones of the limbs are short and broad and give the kimb a shov­el like appear­ance. In the bats of the order Chi­rope­tra, the humerus,radius and ulnaas well as four dig­its are great­ly elon­gat­ed so as to sup­port the wing mem­brane. The fore­limb is thus mod­i­fied for flight . 

exam­ples of homo­lo­gus struc­ture in plants are, a thorn in a boun­gainvil­la Or a rose and a ten­dril in the cucur­bits, are homo­lo­gus, aris­ing as they do in the axil­lary posi­tion.

Analogous Organs

Anal­o­gous organs are mor­pho­log­i­cal­ly dif­fer­ent struc­tures which devel­op in var­i­ous unre­lat­ed organ­isms serv­ing sim­i­lar func­tion. How­ev­er, there are a cer­tain sim­i­lar­i­ties in these struc­ture which are based on adap­ta­tion to per­form the same func­tion. These organs, called anal­o­gous organs, are the con­se­quences of con­ver­gent evolution. 

A clas­si­cal exam­ple of ana­lo­gus organs is the set of wings devel­oped Inde­pen­dent­ly by insects, some extinct rep­tiles as well as birds and bats. The insect wings is a Mem­brane sup­port­ed by chiti­nous veins. The wings of pterosaurs, extinct fly­ing rep­tiles, we’re formed by a fold of skin sup­port­ed by an enor­mous­ly enlarged fourth dig­it of the fore­limbs. In birds, the plan­ning sur­face of the wing is com­posed of feathers. 

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Per­osaurs

The feath­ers are sup­port­ed by an inter­nal skele­ton of bones of the fore­limbs. In bats the wings is formed by a mem­brane mod­i­fied from skin. The wing in the bat is sup­port­ed by the elon­gat­ed and out­spread pha­langes of the last four dig­its of the forelimbs. 

In plants exam­ples are Ten­drils. The ten­drils of pea and vine have dif­fer­ent ori­gin. The for­mer is a mod­i­fied leaf and the lat­ter is a mod­i­fied stem. 

Vestigial Organ

Anoth­er very impor­tant aspects of com­par­a­tive anato­my is the study of ves­ti­gial or rudi­men­ta­ry organ. The pres­ence of ves­ti­gial organs fur­ther strength­ens our notion of spe­ci­a­tion through evo­lu­tion. The ves­ti­gial rep­re­sents struc­ture that were once use­ful to the ances­tors and in course of evo­lu­tion got mod­i­fied in the descen­dents. Such mod­i­fi­ca­tions dur­ing evo­lu­tions are pro­duced as a result of adap­ta­tions to changed envi­ron­men­tal con­di­tions. In many cas­es the reduced organs has assumed a new func­tion , com­plete­ly unlike that for which it was orig­i­nal­ly adapt­ed. In oth­er cas­es, it is appar­ent­ly useless. 

Most wide­ly known exam­ple of ves­tiges is the human ver­mi­form appen­dix. This is a small struc­ture, worm­like in the appear­ance (ver­mi­form) and is the con­strict­ed ter­mi­nal por­tion on the cae­cum of the large intes­tine. In some mam­mals that live on coarse fibrous diet, made up of a con­sid­er­able amount of cel­lu­lose, the cae­cum and appen­dix are Con­sid­er­ably larg­er. This enables the bac­te­ria lodged there­in to enzymeti­a­cal­ly digest the cel­lu­lose. How­ev­er, in humans with changed dietary habits (cel­lu­lose intake is much reduced) the appen­dix has been ren­dered super­flu­ous and there­fore, remains rudi­men­ta­ry. Some­times it is the source of nui­sancd because it’s enlarge­ment result in appen­dici­tis . In man, it can be removed by surgery with­out dire consequences. 

There are numer­ous oth­er exam­ple of ves­ti­gial organs in ani­mals and plants. Nic­ti­tat­ing mem­brane of the eye,the exter­nal ear mus­cle and the wis­dom teeth in humans ‚the ves­ti­gial cau­dal ver­te­brae (embry­on­ic tail) in high­er pri­ma­ry the pelvic gir­dle in whale, Boas ‚pythons, degen­er­at­ed eye in cave dwelling ver­te­brates and inver­te­brates are such exam­ples in animals. 

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Whale

In plants some of the exam­ple of ves­tiges are cov­ered stom­a­ta on the stem of cac­tus, ves­ti­gial leaves in prick­ly pears,the abortive sta­mens of labi­atae and the abortive pis­til­lodes of male flower in Cucur­bitaceae.

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