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Proliferating hybrids were formed between rat spermatids and LM(TK−) cl 1 D, an established line of mouse fibroblasts. Spermatids were obtained from dissociated rat seminiferous tubules by differential attachment of testicular somatic cells to culture plates, followed by gravity velocity sedimentation into linear Ficoll gradients. Cells were fused with the aid of Sendai virus and hybrid selection was facilitated by the inability of cl 1 D cells to grow in HAT medium and the inability of spermatids to attach or proliferate in vitro. Three types of cells grew in fusion plates: (1) unfused contaminant rat testicular somatic cells; (2) rat testicular cell × cl 1 D hybrids and (3) rat spermatid × cl 1 D hybrids. Unfused rat testicular somatic cells were morphologically and karyologically different from either type of hybrid. The 2 hybrid classes were distinguished by the total number of chromosomes and the number of parental chromosome markers. Rat chromosomes are preferentially eliminated from haploid as well as diploid hybrids and at least 3 rat enzymes (lactate dehydrogenase, glucose phosphate isomerase and an unknown oxidase) are synthesized in hybrid clones of both types. The implications of partial haploid hybrids for genetic analysis are briefly discussed.

A clinical and histological study of the lesions occurring in bovine demodicosis in East Africa is described and the pathogenesis discussed.