COITUS. g7 



" 76 septuagenarians gave a proportion, still presenting spermatozoids of 59-5 per 

 100. 



"51 octogenarians gave a proportion, still presenting spermatozoids, of 48 per 100. 



" 4, having passed the age of ninety years, gave entirely negative results." 



The oldest man, in the cases reported by Duplay, was eighty-two, and, in those 

 noted by Dieu, eighty-six years, which latter Dieu fixes as the limit, not having observed 

 spermatozoids after that age. The observations were made by examining the contents of 

 the generative passages twenty -four hours after death. Some of the subjects died of 

 acute, and others, of chronic diseases ; but the mode of death did not present any differ- 

 ences in the cases classed with reference to the presence of spermatozoids. As a result 

 of his own and other investigations, Dieu comes to the conclusion that the power of 

 fecundation in the male often persists for a considerable time after copulation has become 

 impossible simply from incapacity for erection of the penis. 



CHAPTER XXVII. 



FECUNDATION AND DEVELOPMENT OF TUE OVUM. 



Coitus Action of the male Action of the female Entrance of spermatozoids Into the uterus Course of the sper- 

 matozoids through the female generative passages Mechanism of fecundation Determination of the sex of 

 offspring Hereditary transmission Superfecundation Influence of the maternal mind on offspring Union of 

 the male with the female element of generation Passage of the spermatozoids through the vitelline membrane 

 Deformation and gyration of the vitellus Polar globule Vitelline nucleus Segmentation of the vitellus 

 Primitive trace of the embryon Blastodermic layers Formation of the membranes Amniotic fluid Umbili- 

 cal vesicle Formation of the allantois and the permanent chorion- Umbilical cord Membranse decidme 

 Development and structure of the placenta General view of the development of the embryon Development 

 of the cavities and layers of the trunk in the chick External blastodermic membrane Intermediate mem- 

 brane, in two layers Internal blastodermic membrane Neural canal Chorda dorsalis Primitive aortse Ver- 

 tebrae Origin of the Wolffian bodies Pleuro-peritoneal cavity Development of the skeleton Development of 

 the muscles Development of the skin Development of the nervous system Development of the encephalon 

 Development of the organs of special sense Development of the alimentary system Formation of the me- 

 senteryFormation of the stomach Development of the large intestine Formation of the pharynx and oesopha- 

 gus Development of the anus The liver, pancreas, and spleen Development of the respiratory system De- 

 velopment of the face Development of the teeth Development of the genito-urinary system Development 

 of the Wolffian bodies Ducts of the Wolffian bodies and ducts of Muller-Development of the testicles and 

 ovaries Development of the urinary apparatus External organs of generation Hormaphroditism Develop- 

 ment of the circulatory system First, or vitelline circulation Second, or placental circulation Branchial arches 

 and development of the arterial and the venous system Development of the heart Description of the foetal 

 circulation Third, or adult circulation. 



Coitus. 



As far as the male is concerned, coitus is rendered possible by erection of the penis. 

 This may occur before puberty, but, at this time, intercourse cannot be fruitful. As we 

 have seen in a previous chapter, coitus may be impossible in old age, from absence of the 

 power of erection ; but spermatozoids may still exist in the vesicular seminaU-s, and 

 fecundation might occur, if the seminal fluid could be discharged into the generative pas- 

 sages of the female. Coitus may take place in the female before the age of puberty or 

 after the final cessation of the menses, but intercourse cannot then be fruitful. T 

 are sufficiently numerous examples of conception following what woul.l be called imper- 

 fect intercourse, as in cases of unruptured hymen, deformities of the male or- 

 to show that the actual penetration of the male organ is not essential, and that ferimd.i- 

 tion may occur, provided the seminal fluid find its way into even the lower part of the 

 vagina. Conception has also followed intercourse, when the female haa been Insensible 

 or entirely passive ; but we shall consider only the physiology of complete and nor: 

 intercourse, when both the male and female participate, more or less, in the sexual act. 



