522 P- E. Keuchenius, 



half of the abdomen. It is very narrow and invested by two cell 

 layers. The tunica externa (fig. 54 ea;) is very clearly seen. The 

 interna is a rather high epitheUum, which is so developed, that the 

 lumen in a transversal section appears as a fissure (fig. 54). Caudally 

 the ductus ejaculatorius bends to the middle of the abdomen and 

 opens into the chitinous sacculus ejaculatorius (fig. 51 sac) being 

 provided with an apothetes ejaculatorius. A chitinous ductus 

 copulatorius (Fig. 51 d.coj)) is to be found, but I have not been able 

 to follow its course to the end. 



Musca corvina Fab. (Fig. 47 — 50). 



The morphology of the male genitalapparatus of Musca domestica 

 has already been described by Hewitt, who has also given a drawing 

 of it (9, pl. XXVI, fig. 24). The male gonads of Musca corvina do not 

 differ from those of Musca domestica. For convenience sake I give 

 a diagram of the gonads in fig. 47, which I have borrowed from the 

 draAving given by Hewitt. 



The gonads are composed of one pair of piriform testes with their 

 vasa deferentia, ductus ejaculatorius and sacculus ejacula- 

 torius. Hence accessorial glands are missinghere, which is already 

 known to us from the researches of Dufour (6, p. 296). 



The testes (fig. 47 t) are a pair of brown small bodies, which 

 according to Hewitt, are placed transversally with their longitudinal 

 axes and with their pointed ends towards each other. They are situated 

 ventrally of the gut, but what has escaped Hewitt, because he has 

 not made microtomic sections, is that the right testis has its Situation 

 caudally of the left one, the position, therefore, as we have seen in 

 Pollenia rudis. The testes are not enclosed by fat-body-tissue. 

 Two layers invest them: the tunica externa and interna. The 

 externa is a strong brown pigmented, thick layer, in which large 

 nuclei are dispersed (fig. 48 ex). There is no question whatever about 

 chitinous investment, as Hewitt asserts (9, p. 432). He has thought 

 the pigmented tunica externa being of chitin. On the outside 

 tracheal trunks are to be seen very close against the externa. The 

 tunica interna is developed in the blind proximal part of the testes 

 as a membrana propria, but in the distal part the interna appears 

 as a distinct cellular epithelium (fig. 48 in). In several places I saw 

 cellular and tissue-septa, going out from the interna and pushing 

 into the lumen of the testes and being often ramified (Fig. 4:8 sep). 

 In the proximal part the testes are filled up with gono- and cyto- 



