

DEVELOPMENT OF THE FECUNDATED EGG. 499 



can occasion it in parts even at a distance from the pelvic 

 organs. Certain investigations on rabbits (W. Schlesinger) 

 show that excitations of the central portion of the spinal 

 nerves induce uterine contractions ; and the same effect has 

 been caused by excitations of the central portion of the 

 pneumo-gastric ; moreover, clinical observation has shown 

 that a mechanical irritation of the breasts favors uterine 

 contractions. 



II. DEVELOPMENT OP THE FECUNDATED EGG. 



The result of fecundation in the ovum consists of segmen- 

 tation of the vitellus. We commenced our studies with the 

 globular proliferation (p. 10) ; this is a type of one of the 

 manifestations of the general characteristics of the globules, 

 consisting of segmentation and reproduction. Simple seg- 

 mentation can sometimes occur without fecundation; but, 

 generally, the presence of the spermatozoids seems to set in 

 action a physiological excitation which induces the division 

 of the vitelline protoplasm ; in every case of segmentation 

 of the unfertilized ovum, this segmentation does not extend 

 very far, and never forms the blastodermic membrane. 



I. Envelopes of the embryo, respiration, nutrition. 



These envelopes vary according to the period of the 

 development of the embryo ; and, since they are the seat of 

 the exchanges between the foetal organism and its external 

 medium (maternal organism), the manner in which these 

 exchanges (nutrition and respiration) are performed depends 

 upon the different periods of the embryonic life. 



First, After the fecundated egg has traversed the tubal 

 canal, and segmentation of the vitellus has occurred, the egg 

 has no other envelope than its vitelline membrane (see Fig. 

 137) upon whose surface little homogeneous villi are devel- 

 oped ; these constitute the first chorion (Fig. 137, 1). By 

 the process of osmosis and imbibition, the albuminous liquids 

 in the Fallopian tube and the uterine cavity pass through 

 this membrane, and are borne along with the segmentation 

 of the vitellus. 



Secondly, when the segmentation is completed, and the 

 blastoderm is formed, the relations between parent and 

 embryo are more regularly established by the formation of 

 new envelopes and a placenta ; but, in the human species, at 

 this transitional period, there is established a mode of nutri- 



