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The presence of germinal cells outside of the embryonal and fetal gonads of the strepsirhine prosimian Galago crassicaudatus crassicaudatus is described. Forty-three embryos and fetuses from day 26 or 27 of gestational age to near term were studied: more than 90% possessed germinal cells in ectopic sites situated either far from (extragonadal ectopism) or close to the gonads (perigonadal ectopism). The first sites were the walls of the aorta and mesenteric artery, the stroma between the aorta and the cardinal vein, and the retroperitoneal neuroganglia. The second were the mesenchyme dorsal to the gonads and around the vestigia of the mesonephric glomeruli and tubules, and the rete ovarii and testis. The ectopic cells were generally present in conscpicuous numbers, in some animals being more numerous than in the gonads. Those situated far from the gonads underwent degeneration and decreased significantly in numbers during post-embryonal stages of development, while the others remained numerous and functionally active up to near term. While the differentiation of the extragonadal germinal cells after day 60 of gestational age could not be studied due to technical difficulties, the XX and XY cells in perigonadal sites appeared to follow patterns of differentiation identical to those of their entopic counterparts.

This report illustrates some of the errors that may occur during in vivo and in vitro maturation and fertilization of mammalian ova, considers the possible mechanisms accounting for their occurrence, and discusses their functional consequences. Included in the description are anomalies of oocyte and follicular development, i.e., multinucleated oocytes, polyovular follicles, and aberrations of zona pellucida formation. Also considered are deviations from the normal process of oocyte maturation such as chromosomal anomalies, development of abnormal nuclear structures (subnuclei), inhibition of polar body formation and abberations of polar body structure. Anomalies of the process of fertilization such as polyspermia, sperm penetration into polar bodies, and development of multinucleated blastomers in two-cell embryos are also described.

This report demonstrates for the first time the presence of centrioles in a rhesus macaque oocyte which had attained meiotic maturation in culture. The exceptional presence of centrioles in this oocyte was associated with anomalous patterns of chromosomal and spindle organization.

In this study, which was performed on 52 sheep fetuses aged 24 to 85 days, we examined the relationship between testicular development and the "giant" mesonephric nephron, a peculiar structure consisting of a large glomerulus and multiple tubules. The development of the testis occurred in two phases. The preparatory phase began at day 24 of gestation, evolved simultaneously with the involution of the glomerulus of the giant nephron, and was characterized by mobilization of the glomerular cells and by their colonization of the genital ridge. By day 31, a prominent mass of migrating mesonephric cells had developed; it extended uninterrupted from the giant glomerulus into the gonad where the mesonephric cells associated with the germinal cells forming the cellular template from which the testicular cords later became assembled. At complete involution of the glomerulus (day 52), the migratory mass implanted on the tubules of the giant nephron, which thus became continuous with the gonad. During the organizational phase, which began at day 29 with the formation of the tunica albuginea, the various components of this continuum became progressively organized along a testis-to-mesonephros direction into seminiferous cords, tubuli recti, the cords of the rete testis, and the ductules efferentes. These observations show that, in the sheep, the precursors of the Sertoli cells are mesonephric in origin, and that the genital tract proximal to the epididymis differentiates from a single mesonephric nephron.

The morphogenesis of the sexually indifferent gonad of the primate Galago crassicaudatus crassicaudatus was studied by high-resolution light microscopy and electron microscopy in 15 embryos aged 26 to 33 days. Onset of gonadal development follows the morphogenesis of the mesonephros by a conspicuous interval and is identified as the time when the first primordial germinal cells arrive in the region ventral to the central third of the mesonephros; this is followed by intense proliferation of the coelomic mesothelial cells lining the area. They become organized into short piles that deepen in the underlying mesenchyme, enclosing the germinal cells in the process. Rapidly, the piles become confluent forming a compact mass, the gonadal blastema, which is soon cleaved into gonadal cords by stroma and vascular lacunae. The mesonephros becomes involved in the morphogenesis of the gonad only in late stages of development when anatomic continuities become established between the capsules of its regressing glomeruli and the elongating gonadal rete cords. These observations show that in the Galago the somatic cells of the gonadal blastema, i.e., the precursors of the definitive testicular and ovarian sustentacular cells, derive from the coelomic mesothelium in contrast to other mammals, e.g., ruminants and rodents, where they are of mesonephric derivation. This important point is discussed in light of the differences that exist among species with regard to the structural complexity, functionality, and stages of differentiation/involution of their mesonephroi on the one hand, and the time of gonadal development on the other.