REPRODUCTION IN MAN 1373 



the prostatic glands, and the glands of Cowper, form the semen, 

 which is pressed along the urethra by rhythmical contractions, 

 from behind forwards, of the bulbo- and ischio-cavernosi muscles. 

 It has been stated that movements take place coincidently in the 

 uterus, so that its axis more nearly corresponds to that of the vagina. 

 The movement of the semen along the uterus and Fallopian tubes 

 is ascribed by certain observers to an antiperistaltic contraction 

 of these organs. A more important factor is probably the move- 

 ment of the spermatozoa themselves. As we have already seen, 

 these are introduced into the female passage in countless numbers. 

 They will be chemiotactically attracted by the alkaline mucus, secreted 

 by and filling the cervix of the uterus. When they have entered this 

 organ they will meet the downward stream of mucus impelled by 

 the action of the cilia lining the uterus and Fallopian tubes. It seems 

 probable that their reaction to this current is to swim * against it 

 (positive rheotaxis), so that they reach the upper part of the Fallopian 

 tubes or the surface of the ovary itself. Fertilisation of the ovum 

 occurs in most cases in the Fallopian tube, and the fertilised ovum is 

 then carried slowly down the tube into the uterus. 



NERVOUS MECHANISM OF IMPREGNATION. Although, in 

 both sexes, coitus is attended by a high degree of psychical excite- 

 ment, yet it is essentially a spinal reflex, and can be carried out 

 when all impulses from the higher centres are cut off by section 

 of the cord in the dorsal region. The centre presiding over the 

 act is situated in the lumbar spinal cord. The external generative 

 organs, like the bladder, are supplied from two sets of nerve fibres 

 from the lumbar nerves through the sympathetic, and from the sacral 

 nerves. The fibres from the lumbar nerves arise in the cat from the 

 second, third, and fourth, or the third, fourth, and fifth lumbar nerve- 

 roots, and in the dog from the thirteenth thoracic, and the first to 

 the fourth lumbar roots. They run in the white rami communicantes 

 to the sympathetic chain, whence they may take two paths. 



(a) The great majority of the fibres run down the sympathetic 

 chain to the sacral ganglia, whence fibres are given off in the grey rami 

 communicantes to the sacral nerves ; their further course is by the 

 pudic nerves, none running in the nervi erigentes. 



(6) A few fibres go by the hypogastric nerves to the pelvic 

 plexus. 



Excitation of these fibres causes contraction of the arteries of 



* Spermatozoa move in a straight line, at the rate of 2-3 mm. per minute. 

 Thus they might traverse the distance of 16-20 cm. between the os uteri 

 and the trumpet-shaped orifice of the Fallopian tubes in three-quarters of an 

 hour. In animals spermatozoa have been found at the peritoneal end of the 

 Fallopian tubes within an hour or two after coitus. 



