918 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



vesiculae seminales is caused by the newly secreted fluid forcing on, 

 through the influence of the ciliated epithelium and the peristaltic action 

 of the vas deferens, the fluid already formed in front of it ; so that, there- 

 fore, the seminal fluid, being continuously formed by the secreting surface 

 of the testicle, is gradually pushed onward, even in the intervals of sexual 

 excitement, to the vesiculae seminales, where it collects. Ejaculation is, 

 however, due to strong peristaltic contraction of the vasa deferentia and 

 the vesiculae seminales, due to the reflex stimulation of the centre in the 

 spinal cord, which co-ordinates the muscular phenomena of ejaculation. 

 The mechanical stimulation of the sensitive integument of the glans, 

 through action on this centre, leads to rhythmical contraction of the 

 bulbo-caveriiosus muscles and to strong peristalsis of the vasa deferentia 

 and the vesiculse seminales, which discharge their contents into the 

 urethra. At the same time the ischio-cavernosus and the deep transverse 

 muscle of the perineum contract, although the former has no effect on 

 the act of ejaculation, and through their rhythmical contraction the 

 seminal fluid is projected from the extremity of the urethra. The degree 

 of stimulation of the glans which is required to start this mechanism 

 varies very considerably in different animals. In all, the role fulfilled by 

 the male is an active process, the female being passive, although a condi- 

 tion somewhat similar to that of ejaculation also exists in the female. It 

 has been found that at the moment of ejaculation a reflex movement sets 

 in in the Fallopian tubes and uterus resulting in the discharge of a cer- 

 tain amount of uterine mucus into the vagina. This is followed by a 

 rhythmical contraction of the sphincter cunni, which is the analogue of 

 the bulbo-cavernosus and of the ischio-cavernosus and of the deep trans- 

 verse muscle of the perineum, while, at the same time, the uterus is 

 erected by the contraction of its muscular fibres and round ligaments, 

 at the same time descending toward the vagina. In the case of the bull, 

 ejaculation occurs almost immediately after the introduction of the male 

 organ within the vagina of the female, and the to-and-fro movement 

 characteristic of the process in other animals is here absent. This is 

 probably to be explained by the peculiar shape of the penis of the bull. 

 In the first place, as has been stated, the organ increases but slightly in 

 its diameter, and, as a consequence, any friction of the body with the 

 capacious vagina of the female would be at best at a minimum. In the 

 second place, the glans penis of the bull is extremely pointed, and it has 

 been supposed that the glans directly enters the open mouth of the uterus, 

 and that the irritation thus produced is sufficient to start the process of 

 ejaculation. This view is to a certain extent supported by the fact that 

 examination of the female ruminant immediately after the act of copula- 

 tion will disclose the presence of spermatozoa within the uterine cavity. 

 This has frequently been determined to be the case in sheep, where the 



