Simian virus 40 (SV40) adsorbs on rabbit spermatozoa but does not penetrate the cells, as indicated by the absence of radioactive material seen on autoradiography of spermatozoa exposed to 13Hithymidine-labeled SV40. In contrast, after exposure of spermatozoa to labeled SV40 DNA, radioactive material was found in the postacrosomal area of the spermatozoa. Furthermore, when spermatozoa exposed to SV40 DNA were fused with cells of the CV-1 line of African green monkey kidney cells, infectious SV40 was isolated. After uterine insemination of rabbits with spermatozoa infected with SV40 DNA, both unfertilized and one-and two-celled fertilized ova were obtained. When The cells were then washed with KRPA and, in some experimnents, treated with rabbit anti-SV40 serum at dilutions of 1: 50-1:300. The spermatozoa were washed with KRPA and maintained in culture medium for 24 and 48 hr at 37-380C.In some experiments, spermatozoa were exposed to SV40 DNA or to [3H ]thymidine-labeled SV40 DNA at a concentration of 1.0-10.0 gg/107 spermatozoa in the presence of 3% (v v) dimethvl sulfoxide. After incubation of the suspension for 2 hr at 37-380C, the spermatozoa were washed in KRPA and some of the samples were treated with 100 ,g/ml deoxyribonuclease I (DNase), dissolved in synthetic medium, for 0.5 hr at 37-380C under 5% CO2 in air.The spermatozoa were washed again and maintained in culture medium for 24 and 48 hr. The culture medium consisted of the synthetic medium with 20% (v/v)

The fine structure of the zona pellucida of mouse unfertilized egg cells and of mouse embryos was investigated. In addition to standard fixation for electron microscopy, fixation with an addition of ruthenium red was used and found to be especially valuable for the purpose of studying the zona pellucida. The zona pellucida of unfertilized egg cells and of embryos consisted mainly of fibrillar and granular material. There were two layers: a thicker internal and a denser external layer in the zona pellucida of the unfertilized egg cells. The zona pellucida of embryos had, in addition to these two layers, a coarse-grained intimal layer inside the internal layer and a fine-grained peripheral cortical reaction whereas the peripheral layer can be accumulated and modified during the passage of the embryo through the female genital tract. The influence of developmental events and environmental factors on the fine structure of zona pellucida was discussed.

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