[Early embryo orientation by direction of the cardinal point in natural clutches of two ranidae species inhabiting geographically distant regions]. / Orientatsiia rannikh zarodyshei po napravleniiam stran sveta v estestvennykh kladkakh dvukh vidov ranidae, obitaiushchikh v geograficheski otdalennykh regionakh.

The azimuth (the least angle with the north-south direction) of the first cleavage furrow and anteroposterior axes of neurula was measured on projections of photographs of natural clutches. The azimuth distribution of the craniocaudal axis of Rana dalmatina neurulae in clutches from southern Italy and the first cleavage furrows of R. arvalis embryos in clutches from central Russia proved identical. Both craniocaudal axes and first cleavage furrows were mostly oriented from west to east. The azimuth distribution of the craniocaudal axis of R. arvalis neurulae in clutches subjected to repeated cold shock proved to be random. The causes and mechanisms of predominant orientation of the embryos in natural clutches of frogs are discussed. We propose that magnetic sensitivity is acquired by cytoskeleton elements, most likely microtubules, during reorganization in the course of normal development or due to experimental influences.

[Disordered mitoses and extranuclear chromatin in the cells of normally developing embryos of Brachydanio rerio]. / Narusheniia mitozov i vneiadernyi khromatin v kletkakh normal'no razvivaiushchikhsia zarodyshei Brachydanio rerio.

In the cells of normal embryos of zebrafish, Brachydanio rerio, the Feulgen-positive particles were found in the cytoplasm, in addition to the following abnormalities of mitoses: retardation and loss of chromosomes, disorganization of mitotic figures similar to those seen with C-mitosis, condensation and pycnotic transformation of chromatin preceding the cellular death. The dynamics of these phenomena was traced in the course of development starting from the 8 cell stage to the late blastula stage. The high frequency of the above findings, as well as a certain extent of the topological correspondence of abnormal mitoses enable the author to propose that the normal development of bony fishes is accompanied by degradation of the hereditary material in some cells of the embryo. This may constitute a step of differentiation for at least provisional structures of the embryos.

[Sedimentation analysis of cell suspensions]. / Sedimentatsionnyi analiz kletochnykh suspenzii.

Simple methods of measurements of the velocity sedimentation at unit gravity of cells obtained by disaggregation procedure from some fixed tissues are described. The relationship between the velocity sedimentation and cellular volume is discussed.

[Heterogenicity of the intracellular potential of Spirostomum ambiguum infusoria]. / Geterogennost' vnutrikletochnogo potentsiala infuzorii Spirostomum ambiguum

Studies have been made on intracellular potenital of the contractile infusorium S. ambiguum. To immobilize the infusorians, they were embedded into gelatin. This procedure made it possible to record intracellular potential for several hours. Heterogeneity and heterochronism of intracellular potential were demonstrated which reveal themselves in its rhythmic changes and spontaneous shifts up to the inverstion of its sign. Possible morphological correlates of various levels of the potential are discussed.