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Female rabbits were inseminated with spermatozoa which had either been freshly ejaculated or stored for 24 or 48 hr at 5° C. One oviduct of each female was flushed 26 to 28 hr after insemination and hcginjection. The ova were examined and returned to the same oviduct if cleavage had occurred. This procedure did not affect the subsequent development of the ova, as compared with those in the undisturbed oviduct. The number of implantations was counted at 8 days and the number of live foetuses at 20 days of pregnancy. Compared with fresh spermatozoa, the stored samples showed significantly lower fertilizing capacity and the fertilized ova showed significantly higher pre- and postimplantation losses.

Changes were found in the tails of the spermatozoa from a 1½-year-old Jersey bull which conformed to the previously described Dag-defect. The tails were heavily coiled so that transverse sections contained several axonemal units enclosed in the same common cell membrane. The axonemes were abnormal, as one or more of the doublets with the corresponding matrix were lacking, and usually the half of the axoneme containing Fibres 4, 5, 6 and 7 was affected. The central fibres and outer coarse fibres were often affected as well. These changes were generally found in close relation to remnants of the cytoplasmic droplet.In the testes, the spermatozoa were morphologically normal and the changes described seemed to originate in the distal part of the caput epididymidis. The possible aetiology and pathogenesis of the defect are discussed.

Sixteen rabbits were injected with thymidine-3H and tissue sections or spermatozoa smears were evaluated by autoradiography. Two successive ejaculates were collected every second day. Analyses of labelled germ cells in twenty-four testes taken 1 hr to 32 days postinjection showed that one cycle of the seminiferous epithelium required 10·7 ± 0·5 days and that labelled spermatozoa should enter the caput epididymidis 31·4 days post-injection. Labelled spermatozoa were found in the proximal portion of four capita epididymidum 32 days and one caput 33 days post-injection, but not in eleven other capita epididymidum 28 to 31 days post-injection. Labelled spermatozoa first were detected in ejaculated semen from five rabbits on Days 38, 39, 41, 42 and 42. The mean number of grains/spermatozoon in autoradiograms of successive samples agreed closely with the scintillation count activity curve. However, neither curve represented the excretion pattern of spermatozoa labelled as preleptotene spermatocytes. The first samples containing labelled spermatozoa had a low percentage of highly labelled spermatozoa while, through mixing with spermatozoa labelled as spermatogonia, subsequent ejaculates contained up to 55% labelled spermatozoa but individual cell activity was lower. Labelled spermatozoa were excreted over a period of 2 to 3 weeks. Epididymal spermatozoa transit time averaged 9·0 days, but it ranged from 6·6 to 10·6 days even with a uniform semen collection schedule. Combined with autoradio--graphic evaluation of tissue sections or semen smears, intravenous injection of 0·1 to 0·3 mc/kg body weight of thymidine-3H should be adequate for experiments of this type.