222 JOSE F. NONIDEZ. 



once. Waves of contraction were noticeable in one of the ovaries, 

 extending from its tip to the base and caused apparently by the 

 contraction of muscle fibers placed in' the thin connective tissue 

 layer enveloping the organ. At the same time the oviduct ex- 

 panded and contracted rhythmically thus bringing one of the eggs 

 lying near the entrance of one of the paired oviducts into its 

 lumen. The contractions were strong enough to push the egg 

 into the oviduct, and probably the process would have gone 

 further had it not been for the exhaustion brought about by the 

 artificial environment in which the organs were placed. These 

 contractions were very conspicuous in the ovaries of all the flies 

 dissected, whether laying eggs or not, and may be explained by 

 the action of the fluid in which dissection was carried out, or by 

 the action of free oxygen on the muscle fibers of the ovary and 

 oviduct, which take the place of the nervous stimulus in the liv- 

 ing fly. 



The orientation of the egg, when passing through the oviduct, 

 is the same as that in the ovary, the micropyle cone being directed 

 toward the latter. The egg is about three times as wide as the 

 oviduct, which is, therefore, considerably distended when the egg 

 is passing through it. 



These conditions make impossible the fertilization of the eggs 

 in the oviduct. Since the micropyle is not facing the opening of 

 the latter into the uterus, and since the egg is larger than the ovi- 

 duct, any spermatozoa, if present, would be pressed aside by the 

 passing egg in the event of their penetration into the oviduct. 



The size of the uterus is so well adapted to that of the egg that 

 the latter occupies almost entirely its cavity (Fig. 9), the ap- 

 pendages remaining within the oviduct (d), thus blocking the way 

 of any spermatozoa that might enter into the latter when the 

 sperm is poured out of the seminal receptacles during fertiliza- 

 tion. A small space (/) is left in the anterior portion of the 

 uterus, between the walls of the anterior pouch and the surface 

 of the egg, and in this space swim the spermatozoa coming from 

 the seminal receptacles. 



The position of the egg within the uterus is constantly the same 

 in all the flies observed, including several females of Drosophila 

 obscura. The dorsal surface of the egg, where the appendages 



