Scanning-electron microscopy of the development of the head of rainbow-trout (Oncorhynchus mykiss) embryos.

The development of the cephalic region of rainbow trout in the 24th, 30th and 36th stages, corresponding to the table of development by Vernier (1969), was studied using light microscopy and SEM. The 24th stage shows a voluminous cephalic region as a principal feature. At this time, most components of this region have started their differentiation. The 30th stage can be considered as an intermediary phase in the embryonic formation, and it is characterized by the high degree of differentiation between the nervous system and the sense organs. In the 36th stage, the basic final shape of the embryo has been reached. The results of this study show that the differentiation of gill lamellae and the opening of the mouth takes place later than that moment described by other authors. This suggests that development between 30th and 36th stages is a critical survival period for rainbow trout, in which respiratory and digestive functions start.

[Changes in the aortic arch in chick embryos resulting from modified hemodynamic factors]. / Alteración de los arcos aórticos en embriones de pollo como consecuencia de factores hemodinámicos modificados.

Hemodynamic factors acting as modelator agents in the outflow region of great vessels and aortic arches have been studied by many authors. In our study, we have tried to analyse the influence which a modification of some of these factors, as it is an increased blood volume, could cause on truncus and aortic arches, by means of the perfusion of blood from chick embryos of 12-15 days of incubation to receptor embryos between stages 22-29 of HH. We have obtained a malformation percentage smaller than expected, on the basis of bibliographic data, so we now believe that hemodynamic factors, by themselves, don't play a role in the definitive morphogenesis and septation of great vessels and its main branches as important as believed until present time.

Rokitansky's syndrome in association with reno-ureteral abnormalities. Teratogenic period.

A case of Rokitansky's syndrome in association with complete duplication of the right upper urinary tract is presented. From a chronological point of view, the morphogenetic processes of the urinary and genital tract are analyzed. It is supposed that the congenital abnormality is produced between the 30th and 37th day of gestation, because reno-ureteral duplication appears at 30-32 days and involution of the Müllerian structures appears at 37 days.