CONCEPTION. 17 



& conservative effort of the system), may have the most dis- 

 astrous results. 



Impregnation. As the ovum descends the Fallopian tube 

 the changes accompanying or preceding menstruation are 

 taking place in the uterus. Its mucous membrane and all 

 the generative organs of the woman are more or less con- 

 gested, and her sexual emotions are commonly more easily 

 aroused. Unless the act of coition occur this passes off, 

 new mucous membrane is formed, and the organs return to 

 ;a quiet state until the period of the next ovulation. If 

 .sexual congress takes place the vagina, uterus, and oviducts 

 are thrown into reflex peristaltic contractions; and there is 

 frequently an increased secretion by the vaginal mucous 

 membrane. Some of the seminal fluid is received into the 

 uterine cavity, and there, or more frequently in the Fal- 

 lopian tube, meets the ovum. The spermatozoa are carried 

 &long partly, perhaps, by the contractions of the muscular 

 walls of the female cavities, but mainly by their own ac- 

 tivity; from observations made on various lower animals it 

 appears that their movements cease immediately on coming 

 into contact with the ovum, and that one only takes part 

 in fertilization. How this latter occurs in the mammalian 

 ovum is not certain; observations in other groups make it 

 probable that the male element directly fuses in 'whole or 

 part with the protoplasmic mass of the ovum, but no .special 

 opening has been detected in the ztna pellucida of the'' 

 mammalian ovum, which however is traversed by numerous 

 minute channels; some physiologists are inclined to sup- 

 pose that material is merely passed by dialysis from the 

 spermatozoon into the egg-cell. 



The fertilized ovum continues its descent to the uterine 

 cavity, but, instead of lying dormant like the unfertilized, 

 segments (p. 26), and forms a morula. This, entering the 

 womb, becomes imbedded in the new, soft, vascular mucous 

 membrane forming there, from which 'it imbibes nourish- 

 ment, and which, instead of being c^st off in subsequent 

 menstrual discharges, is retained and grows during the 

 whole of pregnancy, having important duties to discharge 

 in connection with the nutrition of the embryo. 



