Abstract
Labeled spermatocytes from locusts killed 0, 1, 2, 3, 4, and 6 days after exposure to tritiated thymidine were examined with the electron microscope to determine their meiotic stage. It was found that tritiated thymidine uptake in young spermatocyte nuclei is completed some 24 hours before synaptinemal complexes are formed. It is concluded that in the locust, premeiotic DNA synthesis is completed well in advance of pairing of homologous chromosomes as marked by the formation of synaptinemal complexes. The G-1 and the S-phase are in the order of 24 hours each, while meiotic prophase lasts four to five days under the conditions used.