534 P. E. Keuchenius, 



20. F. TrLLOCK, The internal anatomy of Stomoxys. Proc. Rojal Soc. London. 



Vol. LXXVII. p. 523. 1906. 



21. K. ZiCK, Beiträge zur Kenntnis der postembryonalen Entwicklungsgeschichte 



der Genitalorgane bei Lepidopteren. Zeitschr. f. wiss. Zool. Bd. XCVIII. 

 S. 430. 1911. 



Explanation of Plates. 



General Abbreviations. 



a, remnant of the apical-cell; in, tunica interna; 



acc, accessorial gland; m, muscle-f ihres ; 



aj), apothetes ejaculatorius; sac, sacculus ejaculatorius; 



hr.c, mother branch cell; seft, septum; 



ch, chitin; sp, spermatozoa; 



cy.c, cytocyst; sp.c, spermatocyst ; 



d.cop, ductus copulatorius ; t, testis; 



d.ej, ductus ejaculatorius; tr, tracheal trunk; 



ex, tunica externa; vd, vas deferens; 



g.c, gonocyst; ves, vesicula seminalis. 



Plate XXIII. 



Fig. 1. Diagram of the male gonads. Eristalis. sc.acc, second pair of 

 small accessorial glands. 



Fig. 2. Microphotograph of the end of the abdomen. Eristalis arbtistorum 

 (ventral side). 



Fig. 3. Transversal section of the proximal part of the testis. Eristalis 

 tenax. n, nucleus; x, place where the externa is nearly unpigmented. 



Fig. 4. Transversal section of the distal part of the testis. Eristalis tenax. 

 y, cellular bodies. 



Fig. 5. Section about the height of line z in fig. 1. Eristalis tenax. sc.acc, 

 second pair of accessorial glands; e.ap, end of the apothetes ejaculatorius. 



Fig. 6. Transversal section of the vesicula seminalis. Eristalis tenax. 



Fig. 7. Transversal section of the accessorial gland. Eristalis tenax. 



Fig. 8. Microphotograph of the male gonads. Syrphus Ribesi. The ac- 

 cessorial glands are not to be seen. On the back-ground the gut. 



Fig. 9. Diagram of the male gonads. Syrphus Eibesi. u.vd, unpaired 

 vas deferens. 



Fig. 10. Longitudinal section of the testis. Syrphus Ribesi. y, yolky 

 Clements and between them spermatozoa. 



Fig. 11. Section of the accessorial gland. Syrphus Ribesi. 



Transversal section of the unpaired vas deferens. Syrphus Ribesi. 

 Longitudinal section of the testis. Syrphus baüeatus. n, nucleus. 

 Transversal section of the vas deferens. Syrphus balteatus. 

 Diagram of the male genitalia. Rhingia rostrata. u.vd, unpaired 



