LAMPENBURSTENCHROMOSOMEN UND MULTIPLE NUKLEOLEN BEI ORTHOPTEREN

Isolated unfixed chromosomes from the oocytes of several grasshopper species, of Gryllus domesticus, and of two cockroaches have been investigated under phase contrast. As demonstrated previously in Locusta migratoria, these chromosomes resemble the lampbrush chromosomes in amphibian oocytes. From these the lateral loops of the orthopteran chromosomes differ in that they are only one third as long. The distinctness of chromomeres and chiasmata is considerably lower than that in amphibian oocytes. Besides the lampbrush chromosomes the oocyte nuclei of Orthoptera contain several hundred spheres or granules which are thought to be the multiple nucleoli. In young oocytes, these nucleoli are vacuolated spheroids aggregated compactly in the center of the nucleus. In the oocyte of the cricket, this center contains Feulgen-positive material which disappears in the early growth period when the nucleoli transform from solid structures to several hundred spheres. In oocytes of an intermediate size, both in the grasshoppers and Gryllus such spheroids are present. In the larger mature oocytes the spheres are localized peripherally around the nuclear envelope (Decticus; ), or they become extended into beaded ring forms (Gryllus). or these rings are opened, stretched and connected in a row to form long "pearl-string" threads (Locusta, Acrida, Homorocoryphus). The spheroids around the nuclear envelope of Decticus look very similar to the solid and spheroidal nucleoli in young oocytes of the axolotl. The beaded rings of Gryllus resemble the ring-shaped nucleoli in the amphibian oocytes during their intermediate growing phase.[long dash]Following Keyl''s hypothesis for the construction of replication units, there different appearances of multiple nucleoli are proposed to be results of a similar mode of extra-replication, but of different arrangement. In the case of Gryllus and Decticus the nucleolar DNA arangements are set free from the chromosomes, but they remain attached one behind the other in Locusta and some other grasshoppers.