A very rare developmental anomaly showing bilaterally persistent sciatic arteries was found in a cadaver of 89year old female. Both right and left sciatic arteries arose from the internal illiac arteries and appeared between the piriformis and superior gemellus muscles at the buttock, being about 10 mm in diameter. Each artery, which accompanied by the companion vein, i. e. sciatic vein, sent the branches to the gluteus maximus and the flexor muscles of thigh. On the other hand, the femoral arteries of both lower limbs were smaller than usual, measuring 4.7 mm in left and 5.2 mm in right. The terminal vessels of those were joined to the sciatic arteries at the popliteal fossa. In addition, the present case also had another developmental anomaly, i. e. superficial brachial artery in the right upper limb.
Germ cells of the chick ovary which develop asymmetrically on the right and left sides of the embryo were observed by electron microscopy from 7 to 17 days of incubation. Germ cells showed different patterns in the right and left ovaries, and also differences in the cortex and in the medulla. At 7 to 9 days, germ cells were individually present in both the right and left ovaries. They proliferated from 10 days onward and formed many cell aggregates. In each aggregate, germ cells were joined by intercellular bridges, and their cell cycles were synchronized. Although meiotic features of the germ cells were frequently found in the cortex of the left ovaries at 16 days, some germ cells exhibited these features at earlier days. In the meiotic germ cells, the "Balbiani body," which was composed of a concentration of cell organelles shifted to one pole of the cell, was always seen. The appearance of a meiotic nucleus and Balbiani body was characteristic of germ cells located in the left ovarian cortex, whereas those were never seen in the left medulla and in the right ovary. At 16 and 17 days, some germ cells were released into the lacunae of the medulla of both the right and left ovaries. The meaning of this phenomenon is discussed. Degenerating germ cells were frequently observed in the right ovary, but rarely in the left.
The intraembryonic blood islands preceding the hepatic haemopoiesis, were examined in embryos from stage 17to 19 by light microscopy, and their three-dimentional expansion was demonstrated. These blood islands were located in the mesenchyme of the lateral fold, mesentery, allantois and ventral aorta, commonly showing large scale. Except the lateral fold, however, those were just temporary sites. Particularly large islands were necessarily found in the mesenchyme of the lateral fold at the stages examined. They were present bilaterally and exhibited cephalocaudally long, rod-like structures with variable sizes. The largest island measured over 2,600 μm in length.
Abstract Chick primordial germ cells (PGCs) which separated from the “germinal crescent” entoderm in the period from stages 4 to 8 circulated mostly through the developing blood vessels from stage 10 onward and finally migrated into the gonad. The PGCs making their appearance up to this stage were generally spherical in profile, about 14 μm in diameter. Some of the PGCs, in contrast, did not enter the blood vessels but remained in the tissue (mesenchyme) of the embryo proper (tissue PGCs) and possessed pseudopodial processes, suggesting their migration by means of amoeboid movements. The circulating PGCs emerged from blood vessels in the vicinity of developing gonads by three days (gonadal PGCs). The principal mechanism responsible for the subsequent migration of gonadal PGCs is assumed to be amoeboid movements as in the case of tissue PGCs. Notable amounts of PAS‐positive glycogen were demonstrated in the cytoplasm of PGCs in all stages observed. They also contained yolk and lipids intracytoplasmically, the former dissipating in relatively early stages of development. Electron microscopic observation revealed the electron‐opaque, “fragmented nucleolus” in the large nucleus (8 μm in diameter), which represented another prominent feature of chick PGCs. PGCs contained a well developed Golgi complex and endoplasmic reticulum.
Chick primordial germ cells (PGCs) in the final course of their migration were observed by scanning (SEM) and transmission (TEM) electron microscopy, with an emphasis on their extravasation. The profile of the PGCs leaving blood vessels were first revealed under SEM. Chick embryos at stages 16 and 17 (about 2.5 days of incubation) were employed for the present study, since the PGCs emerging out of the vessels in teh gonadal area could be observed in high frequency at this developmental period. PGCs in the vessels showed a round profile, possessing many microvilli, while extravasating PGCs were rather oligovillous except the one side of the cell, where long filopodia extended toward the wall of the vessels. These filopodia seem to adhere to the wall of the vessels prior to emerging out. After extravasation, PGCs moved toward adjacent prospective gonadal epithelium and invaded it by amoeboidism. Following the settling down in the epithelium, PGCs showed rugged surface with few microvilli.
Chick embryos from stage 15 to stage 18, which is the most frequent extravasation period, were investigated by means of serial sections and light microscopy in order to learn the detailed relationship between the settlement sites of the primordial germ cells (PGCs) and the forming genital ridge. PGCs circulating in the vascular system came out of the small vessels in the splanchnopleure posterior to the vitelline artery. This PGC extravasation was limited to an area about 1.2 mm caudal to the vitelline artery. After the extravasation, the PGCs entered the neighboring thickened coelomic epithelium of the splanchnopleure. This thickened epithelium, which had incorporated the PGCs, changed the location toward the future gonadal site with the advance of development. At stage 16, the thickened portion of the epithelium was located in the splanchnopleure; then it moved toward the somatopleure via the coelomic angle; finally, at stage 18, this epithelium occupied the region between coelomic angle and the mesonephros which corresponded to the future genital ridge. This means that the thickened epithelium of the splanchnopleure which initially incorporated the PGCs becomes the superficial epithelium of the genital ridge in more advanced stages. The thickened portion of the epithelium of the splanchnopleure at stage 16 is thought to be the definitive gonadal anlage.
