Resumido por el autor, Royal Kort,oxi Chapman.Estudio Lobre la correlacih entre la estructura de la pelvis J' las costumbres de algiinos mainiferos cavadores.En el preserite traloajo se doseriben y estudian Ins pelvis de 10s iriamiferos cavadoreq y segdn la estructura de dichos huesos se clasifican en cavadoras tipicas' (topos, musarafias, Geomys, y algiunas especies de Microtus) en las cuales 10s bordes ventrales de 10s huesos pubianos son horizontales y divcrgcn posteriorrnente y In sinfisis falta en absduto o, si exis te, estii forrnada por una barra 6sea transversal ; las ' semi-cavadoras' (m'uchas especies de ratones, algunos insectivoros), en ias cuales 10s h e w s pubiarios e&n inclinados caudo-vei~t~.a~,lmente y convergen para formar una sinfisis en sus puntos de contacto. Las pelvis 'cavadoras tipicas' sc lian dividido en las de 'tipo estrcclid (topos musarafias) y las de ' tipo ancho' JGeom,ys, topos marsupiales J' otros). La sinfisis pubiana puede existir o faltttr en las liembrus de Geomys perteneeientes a la misma especie. Todas estas pcrvis son horizontales y coosificadas con la columna vertebral, y de este niodo dirigen la fucrza producida por 10s niierribros posteriores a1 cavar, a lo largo de una linea recta paralcla a la columria vertebral. La capacidad de la pelvis es, por consiguiente, tan liniitada que os necesaria la desaparicih de la siiifisis pubiana para perriiitir el paso del feto durante el parto. La falta de sinfisis pubiana cstA compensada en el soporte de las visceras por el cruzamiento de 10s mGsculos rectos del abdomen-el mhculo dcrecho se inserta en el liueso pubiano ieyuierdo y el indsculo cie este lado en el misrno hueso del lado derecho. Estas estructuras paralelas que se presentan en 10s diferentes grupos de animales de costumbres sexnejantes, indican la iinportancia dc fuerzas similares, yue actuhn de un rriodo semejante, como factores de la modificacih de la estructura.
The confused flour beetle (Tribolium confusum) was chosen for this study because it lives in a food which ordinarily contains no living organisms. The death rates are greater in cultures which are handled daily than in those which are not handled but when all are handled alike the results are comparable.
The results from experiments with individual beetles in various kinds of flour were plotted with instars (larval stages) on the ordinate and time in days on the abscissa, using the results from control experiments in wheat flour to determine the length of the various instars from an "x = y" formula. The curves of development were found to be straight lines throughout all but the last instar. The curve for the last instar during which the larva transformed deviated from the straight line in certain foods, notably rice flour.
When mass cultures were used the death and transformation curves were plotted for each synthetic food. A comparison of the curves from wheat flour and the synthetic foods shows that the first parts of the curves are very much alike in all cases and that a few resemble the control in every respect except that the transformation curve has been moved back for a considerable time.
The death curves for the mass cultures are not smooth but show sudden increase in death at approximately the times of molting. These curves may therefore be compared with the records from individual beetles.
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