GROWTH OF EMBRYOS OF THE COMMON VOLE MICROTUS-ARVALIS(PALL)

Assuming a uniform distribution of the vertex-coccyx length frequencies in the investigated embryos of wild populations of Microtus arvalis (Pall.) and on the basis of data from the literature, a function of embryo growth was determined: y = exp(-0,88 + 0,2x) where y = vertex-coccyx length of embryos (mm), x = age of embryos (days). According to the calculations, pregnancy is recognised not before the 4th day after conception. With a pregnancy period of 21.56 days, the macroscopically determined portion of pregnant females should be multiplied by a factor of 1.17 in order to obtain the actual rate of pregnancy.