Previous studies have shown that when Domesticated Rabbits (Oryctolagus cuniculus) were inseminated with sperm of the Cottontail Rabbit (Sylvilagus floridanus) about 30% of the ova were fertilized (Chang and McDonough, '55; Chang, '60). When domesticated rabbits were inseminated with European Hare (Lepus europaeus) sperm practically all the ova were fertilized (Adams, '57; Chang and Adams, '62). In both cases, however, all the fertilized ova degenerated before or at the time of enlargement of the blastocysts. This paper reports ( 1 ) the fertilization of domesticated rabbit ova by sperm of the Snowshoe Hare (Lepus americnnus), ( 2 ) the possible fertilization of a snowshoe hare ovum by rabbit sperm, and ( 3 ) the proportion of rabbit ova fertilized by rabbit or hare sperm following insemination of a mixture containing equal numbers of their sperm.
A research project supported by the Atomic Energy Commission was undertaken in this laboratory to investigate the effects of irradiation on mammalian ova in vitro. I n order to develop needed techniques and to comprehend the effect of radiation on germ cells in general it was thought profitable to first study the effect of radiocobalt irradiation on spermatozoa in vitro.I t is known that during spermatogenesis the male germ cells are extremely sensitive to irradiation while the mature spermatozoa are extremely resistant to such exposure. X-irradiated spermatozoa may retain both their motility and fertilizing capacity but are unable to initiate normal development of the fertilized ova due to latent damage to the chromatin. I n their extensive study of the effects on embryonic development of X-irradiation of rabbit spermatozoa in zdro, Amoroso and Parkes ('47) concluded that exposure of spermatozoa to 50 r and 100 r did not interfere with fertilization, segmentation of the ovum, or embryonic and fetal development ; following irradiation with 500 r, litter size was reduced and with 1,000 r no implantation "as observed; with 2,500 r all tuba1 ova
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