The distribution of intermicrotubular bridges in meiotic spindles of the crane fly

The distribution of intermicrotubular bridges in spindles of tipulid spermatocytes (Pales ferruginea, first meiotic division) was analyzed using serial sections of preselected cells. Bridges were found in all spindle regions, including kinetochore microtubules and free microtubules in the chromosome fiber. The dimensions of bridges were variable, ranging between 60 and 300 Å in length and 40 and 190 Å in thickness. Bridges seem to be randomly distributed. No accumulation in or absence from particular spindle regions was detected. Quantitative analysis revealed a linear, positive correlation between the number of microtubules and the number of microtubule pairs capable of forming bridges and, on the other hand, between microtubule pairs and intermicrotubular bridges. The possible composition and significance of bridges are discussed.