Untersuchungen zur Mustergliederung in fragmentierten Primordien des männlichen Geschlechtsapparates von Drosophila séguyi

Abstract

1. 1. Genital disks of mature larvae of Drosophila séguyi were implanted in larvae of D. séguyi and D. melanogaster and their developmental performance compared with in situ genitalia. In a qualitative sense there were no differences between experimental and normal in the investigated structures (anal plates, claspers, penis, apodeme, anterior and posterior parameres, decasternum, hypandrium). 2. 2. In addition to slight differences in size of the developing implants, 2 to 5 extra bristles often occur as new formations on the proximal border of the decasternum. This never occurs in situ. 3. 3. Median and paramedian fragmented disks were implanted into host larvae of different ages. The regulation of these fragments and with it the plan of the anlage agree essentially with the findings of Hadorn et al. (1949) and Ursprung (1959). 4. 4. There is a definite time sequence in the appearance of the single structural elements during the course of regulation which is characteristic for the 1 2 and the 3 4 implants. 5. 5. The 3 4 fragments which form anal plates on their cut sides were classified on the basis of their size into 5 steps of potentiality. The bristle pattern developed in each step was investigated according to its composition. Only the bristle pattern of the fifth step of realization develops harmoniously, although in miniature. The disturbed pattern of the third and fourth steps is considered dependent upon the special dynamics of formation of the anal plate. 6. 6. In addition to the regular bristle elements of the different types intermediate, compound bristles were also formed between them, both in small experimental plates and in anal plates developed in situ. From this finding a diffusible substance for the pattern formation is postulated whose concentration decreases in a gradient from the mediodistal cut edge laterally and proximally across the newly formed blastema. 7. 7. The developed potentialities of 1 4 fragments vary considerably when tested in hosts of various ages. Only in young hosts are these lateral fragments able to form miniature but qualitatively normal genitalia. 8. 8. The fragmentation experiments show that the penis develops on the basis of an all-or-none reaction. They also reveal that the appendages of the penis (anterior and posterior parameres) are able to differentiate their normal shape and size in the absence of the field responsible for the development of the penis. 9. 9. The shape of the decasternum is determined by the structural elements surrounding it. 10. 10. In order to account for both the unpaired, median hypandrium as well as the paired penis appendages one may postulate paired fields lying in the lateral portions of the genital disk. The appearance of a hiatus interrupting the hypandrium in more primitive Drosophilidae as well as in melanogaster females, modified by the transformer-gene ( tra), support the concept of paired fields.