There is now abundant evidence in a wide range of mammalian and non‐mammalian species to show that the relative size of the testis and the morphology of the spermatozoa are infallible predictors of the mating system. Species with the largest testis/body weight ratios and the best spermatozoa have a multi‐male or promiscuous mating system in which sperm competition operates. Judged by these criteria, men were not designed to be promiscuous. There is increasing evidence in humans to show that most spontaneous mutations of the germ line occur in the testis. Because these provide the variability on which natural selection can operate, the testis holds the key to evolution. Genes on the Y chromosome that control male fertility are particularly prone to mutations, perhaps because of the mutagenic metabolites produced by the metabolically active testis. Testicular descent into a scrotum, and cooling by countercurrent heat exchange between the spermatic artery and vein may have evolved as a way of holding the mutation rate in check. The hormones secreted by the testis, which control libido and aggression, ensure that these male mutations are disseminated as widely as possible throughout the population.

No abstract

The ultrastructure of four roe-deer blastocysts at different stages of embryonic development were studied. During delayed implantation, the outer surface of the trophoblast possessed numerous microvilli and periodic invaginations or caveolae. There was a marked lack of organelles such as mitochondria or endoplasmic reticulum in the cytoplasm of the trophoblast cells, though many lipid droplets, granular inclusions and a lamina of fine fibrillae were present. Elongation of the blastocyst was associated with a decrease in the size and number of the microvilli, the disappearance of lipid droplets and granular inclusions, a reduction in the amount of fibrillar material and a dramatic increase in the development of mitochondria, granular endoplasmic reticulum, ribosomes and Golgi apparatus.The histology of the ovaries and uterus was studied in thirty-one roe deer. No prominent changes occurred in the ovaries at any stage of development; all ovaries possessed active CL and showed signs of follicular growth and atresia. Changes in the degree of mitotic activity, epithelial cell height, endometrial vascularity and stromal oedema were observed in the uterus throughout the period of delayed implantation and during the phase of rapid embryonic growth. Elongation of the embryo was associated with a marked decline in the height of the glandular epithelium and an increase in endometrial vascularity.The most important ultrastructural changes in the uteri of six roe deer were observed in the endometrial glands. Delayed implantation was associated with the accumulation of numerous supranuclear vesicles derived from the Golgi apparatus, while the resumption of embryonic growth was correlated with their sudden disappearance. When elongation had

No abstract

Thirty female dromedary camels were inseminated on a total of 50 occasions with 2^4 ml of fresh guanaco semen diluted with an equal volume of commercially available camel semen extender. Similarly, nine female guanacos were inseminated on 34 occasions with 4^6 ml of fresh, diluted camel semen. Only two of the dromedary females conceived; one aborted a female foetus on day 260 of gestation and the other gave birth to a stillborn female calf on day 365. Six conceptions occurred in the female guanacos. Two of these conceptuses, diagnosed by ultrasound, were resorbed between days 25 and 40 of gestation, one female foetus was aborted on day 291, another female foetus was aborted on day 302, and one female calf was stillborn on day 365 of gestation. The sixth foetus, a male, was born prematurely but alive after a 328-day gestation. It had a phenotypic appearance intermediate between that of a camel and a guanaco and its hybrid parentage was con¢rmed by the DNA ¢ngerprinting of eight llama microsatellites. To our knowledge, this is the ¢rst viable hybrid ever to be produced between Old World and New World camelids, which have been reproductively isolated from one another for at least 11 million years. The preponderance of female hybrids is in accordance with Haldane's law. Histological examination of their ovaries revealed a failure of meiosis, with only an occasional abnormal oocyte surrounded by follicle cells. Although the diploid chromosone number of camels and guanacos is the same (2n 74), su¤cient genetic change has taken place to make the pairing of homologous chromosomes no longer possible.