Rio de Janeiro – Planaria

Text:

The existence of a division of the genus Planaria which inhabits the dry land, interested me much. These animals are of so simple a structure, that Cuvier has arranged them with the intestinal worms, though never found within the bodies of other animals.

Numerous species inhabit both salt and fresh water; but those to which i allude were found even in the drier parts of the forrest beneath logs of rotten wood, on which i believe they fed. In general  form they resemble little slugs but are very much narrower in proportion and several of the species are beatifully colored with longitudinal stripes.

Their structure is very simple, near the middle of the under, or crawling surface there are two small transverse slits, from the anterior one of which a funnel shaped and highly irritable mouth can be protruded.

For some time after the rest of the animal was completely dead from the effects of salt water or any other cause, this organ still retained its vitality. 

I found no less than twelve different species of terrestrial Planariae in different parts of the southern hemisphere. Some specimens, which i obtained at Van Dieman’s Land, i kept alive for nearly two months feeding them on rotten wood. Having cut one of them transversaly into two nearly equal parts, in the course of a fortnight both had the shape of perfect animals. I had, however, so divided the body that one of the halfs contained both the inferior orifices and the other, in consequence, none.

In the course of 25 days from the operation, the more perfect half could not half been distinguished from any other specimen. The other had increased much in size and towards it’s posterior end a clear space was formed in the parenchymatous mass in which rudimentary cup-shaped mouth could clearly be distinguished; on the under surface, however, no corresponding slit was yet open. If the increased heat of the weather as we approached the ecuator had not destroyed all the individuals there can be no doubt that this last step would have completed its structure.

Although so well-known an experiment it was interesting to watch the gradual production of every essential organ, out of the simple extremity of another animal. It is extremely difficult to preserve these Planariae; as soon as the cessation of life allows the ordinary laws of change to act their entire bodies become soft and fluid, with a rapidity which i have never seen equalled.

Traducere:

Ma interesa existenta unei diviziuni a genului Planaria. Aceste animale au o structura atat de simpla incat Cuvier i-a aranjat impreuna cu viermii intestinali, desi nu au fost gasiti niciodata in corpul altori animale.

Numeroase specii traiesc atat in apa sarata cat si in apa dulce, dar cele la care ma refer au fost gasite chiar si in cele mai uscate parti ale padurii, sub trunchiuri putrezite de copaci, cu care cred ca se hraneau. Ca forma generala seamana cu mici limacsi, dar sunt mai ingusti si cateva specii sunt colorate cu dungi longitudinale.

Structura lor e foarte simpla, la mijlocul suprafetei pe care se tarasc, sunt doua mici taieturi transversale iar din cea anterioara se vede o gura puternic iritabila in forma de con.

Chiar si la un timp dupa ce animalul a murit datorita efectelor apei sarate sau altor cauze, acest organ continua sa-si mentina vitalitatea.

Am gasit nu mai putin de 12 specii diferite de Planarii terestre in diferite parti ale emisferei sudice. Pentru mai bine de doua luni am pastrat vii cateva dintre specimenele obtinute din Van Dieman’s Land, pe care le-am hranit cu lemn putrezit. Atunci cand am taiat transversal in parti egale un specimen, ambele parti aveau forma unui animal perfect dupa numai o noapte. Totusi, eu divizasem corpul in asa fel incat una dintre jumatati continea ambele orificii inferioare si cealalta, in consecinta, niciunul.

Dupa 25 de zile de la operatie, jumatatea care continea orificiile nu putea fi distinsa de orice alt specimen. Cealalta crescuse mult in marime si catre partea posterioara se putea observa un spatiu in masa parenchimatoasa in care o gura in forma de cupa putea fi usor distinsa; pe suprafata inferioara, nu exista nici o deschizatura. Daca temperatura crescuta, din zona ecuatorului nu ar fi distrus indivizii nu am nici un dubiu ca acest ultim pas ar fi completat structura.

Desi e un experminet bine-cunoscut a fost interesant de urmarit productia graduala a fiecarui organ esential, din extremitatea unui alt animal. Este extrem de dificil sa conserv aceste Planarii; imediat ce incetarea vietii permite procesele naturale ale schimbari, corpurile lor devin moi si fluide cu o rapiditate pe care nu am mai vazut-o pana acum.

Comentarii:

Am vrut sa arat si partea efectiva de lucru a lui Darwin in expeditie, micutele animale cu care se juca au fost supuse la diverse experimente, care desi cu nimic spectaculoase l-au ajutat sa inteleaga capactiatea de regenerare a unor specii.

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