Studies Of Inheritance In Guinea Pigs And Rats PDF Download

Excerpt from Studies of Inheritance in Guinea-Pigs and Rats For several years I have been engaged in studies of heredity in guinea-pigs. In the course of these studies all the common varieties of guinea-pigs have been investigated by the method of experimental breeding and something has been learned concerning their interrelationships and probable mode of origin. The actual origin of most of these varieties is, however, unknown, as is true also concerning most varieties of domesticated animals. One or two varieties have, however, been made synthetically in the laboratory and it is conceivable that, if we had the original wild stock to work with, from which the domesticated guinea-pig has arisen, some or all of the existing varieties might be synthesized anew and perhaps still others might be obtained, and that in this way something might be learned of the method by which new varieties arise. From considerations such as these I have for several years been seeking to obtain living specimens of the wild species which most closely resemble guinea-pigs. In 1903 I received from Campinas, Brazil, 3 wild-caught individuals referred at the tune to the species Cavia aperea, but since found to agree better with the description of C. rufescens. From two of these animals young were obtained, and crosses, the results of which have been described in detail by Dr. Detlefsen (1914), were made with domesticated guinea-pigs. It may be noted that all male F1 hybrids were sterile, but that the F1 females were fertile, and that upon repeated crossing of these with male guinea-pigs, a race of fertile hybrids was at last obtained, these being, in the language of breeders, about guinea-pig, rufescens. From this result it seems doubtful whether C. rufescens has any close genetic relationship to the domesticated guinea-pig, although by hybridization it has been found possible to produce races ( or more guinea-pig) which have derived certain characters from a rufescens ancestor. Cavia aperea from Argentina has been crossed with the guinea-pig by Nehring (1893, 1894) in Berlin, with the production of fully fertile hybrids. This result indicates a closer relationship with the guinea-pig than C. rufescens manifests. Darwin (1876), however, did not regard aperea as the ancestor of the guinea-pig, because he found it to be infested with a different species of louse. I have not myself been able as yet to obtain specimens of C. aperea. Nehring (1889) has argued with much plausibility that Cavia cutleri of Peru is more probably the ancestor of the guinea-pig, for (1) it agrees closely with the guinea-pig in cranial characters and it occurs in a region where guinea-pigs have been for a long time kept in domestication, as is shown by the occurrence of mummified guinea-pigs which had been buried with the dead. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works."