Abstract
1. The heterochromosomes of crane-flies (Tipulidae) are sex chromosomes (XY in males), as could be demonstrated by the sex limited inheritance of Y-autosome translocations in Tipula oleracea, Pales crocata and P. ferruginea. 2. Like the majority of tipulids the species more closely studied in the present contribution, P. ferruginea, possesses 3 pairs of large autosomes and small XY chromosomes, which are heteromorphic. 3. The normal strain of P. ferruginea contains two types of size-different X-chromosomes, Xl and Xk, of a length ratio of 1∶1,4. They show normal mendelian inheritance and are viable in all combinations. X-chromosomes of different length have also been observed in Tipula paludosa and T. oleracea. 4. Triploid larvae with normal spermatogenesis have been found in Tipula paludosa, Pales lunulicornis, and P. ferruginea. The triploid individuals of the two Pales species possess the sex-chromosome combination XXY. 5. In P. ferruginea a strain with supernumerary sex chromosomes has been found. In crosses of XYY males of this strain with normal XX females, besides XX females, XY and XYY males, also XXY males occur which are fertile. Their occurrence proves the existence of an epistatic male determining factor (or factors) in the Y. Presence or absence of Y thus is responsible for sex realisation.
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