The Growth of the Locust Embryo

Abstract

ABSTRACT Three measures of the growth of the embryo of Locusta migratoria migratorioides (R. & F.) were determined from the third to the twelfth days of development at 30° C. These measures were the dry weight, reduced weight, and number of nuclei. Measurements of the density of the embryo were also made and used with the R.W. to calculate the wet weight. The same measurements of the intact egg were taken throughout development. The growth in dry weight of the locust embryo from the third to twelfth days of development appeared closely comparable with that of vertebrate embryos such as the chick embryo and could be described by the usual double logarithmic relation with growth constants of closely comparable values. Increase in R.W. and wet weight could be similarly described from the third to ninth days after which the rate of increase fell away more rapidly than expected. Increase in nuclear number occurred at a higher rate than any of the other measures up to the ninth day after which no further increase above a total of about two million nuclei could be detected. As in some vertebrate embryos, cell multiplication seemed not to parallel growth in weight. The implications of the differences in rates of increase of these measures were considered. From the third to ninth days the embryo was approximately 90 per cent, water, the density of the dry material may have increased and the dry weight per nucleus decreased rapidly to a constant value. After the ninth day there appeared to be a fall in water content and dry density and an increase in the dry weight/nuclear number ratio. The density of the wet embryo increased steadily after the sixth day. The total loss in dry weight of the egg due to respiration was about 20 per cent., an amount typical of many insect eggs. The eggs increased in weight by about 120 per cent., chiefly during the fourth and fifth days. The percentage water content rose from about 50 per cent, to about 80 per cent. Changes in the density of the eggs reflected perfectly the changes in water content. The R.W. of the eggs was constant except for a rise of about 40 μ g. during the fourth and fifth days. It was suggested that this could be accounted for by the presence in the chorion of about 0 04 /xl. of air which was displaced when water uptake took place after the third day. This would also have accounted for the very small difference in the measured changes in density compared with those calculated from the water intake. A constant R.W. and a large decrease in dry weight imply that the density of the dry material of the eggs must have increased at the same rate as the respiratory loss in dry weight. Combustion of fat might account for this.