. The effects of inbreeding and crossbreeding on guinea pigs : III. crosses between highly inbred families. may be due in part to a direct causal relation. Still-born young are naturally considerably lighter than young born high birth weights of the progeny of crossbred dams might thusbe due merely to their rehitively small percentage of stillborn complication is avoided by comparing the birth weights of onlythose young which reach 33 days Fig. 12). We find, in fact, that. 11.—The birth weight of all young born, 1916-1919. Indices correcting for effects of size of Uttera
. The effects of inbreeding and crossbreeding on guinea pigs : III. crosses between highly inbred families. may be due in part to a direct causal relation. Still-born young are naturally considerably lighter than young born high birth weights of the progeny of crossbred dams might thusbe due merely to their rehitively small percentage of stillborn complication is avoided by comparing the birth weights of onlythose young which reach 33 days Fig. 12). We find, in fact, that. 11.—The birth weight of all young born, 1916-1919. Indices correcting for effects of size of Utterand seasonal conditions (Table 2). (See Fig. 8 for explanation of symbols.) the differences among the experiments are reduced. Neverthelessthe essential points noted above are still present. It seems clearthat the prenatal rate of growth depends largely on the character-istics of the dam as far as it depends on heredity at all. The heredityof the young, however, seems to be more important than in the caseof the percentage born alive, as indicated by the records of Experi-ments CO and CA in comparison with the inbreds. That the agree-ment in the standing of the crossbreeding experiments in relation tothe total inbreds in the two respects, birth weight and percentageborn alive, does not rest on a common physiological factor is shownby the lack of agreement among the separate inbred families. Experiment CG, in which the parents were selected because oftheir exceptionally great weight at we
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