SEX IN LIVING FOEMS 107 



narrow tube referred to, called the Fallopian tube, and 

 passes down into the cavity of the uterus. If fecunda- 

 tion does not occur, it is expelled or absorbed after six 

 to twelve or fourteen days. If copulation occurs, how- 

 ever, zoosperms are brought into the cavity of the 

 uterus, and, coming in contact with the ovum, fecun- 

 date it. This is conception. When the natural process 

 is allowed to proceed, development occurs. 



Gestation, or Pregnancy.— This is the term applied 

 to the process last referred to. We shall not attempt 

 to describe in detail this most wonderful and intricate 

 of all living processes; but will sketch only the chief 

 points, leaving the reader who would obtain a more 

 complete knowledge of the subject, to consult any one 

 of the numerous physiological and obstetrical works 

 which deal with it in a very exhaustive manner. 



As soon as the ovum is impregnated by the male 

 element, it begins a process of symmetrical division. 

 The first division produces two cells out of the single 

 one which first existed. By the next division, four 

 segments are produced ; then eight, sixteen, etc. While 

 this process is going on, the ovum becomes adherent to 

 the internal wall of the uterus, and is soon enveloped 

 by its mucous membrane, which grows up about it and 

 incloses it. 



The Primitive Trace.— Wlien the process of seg- 

 mentation has advanced to a certain point, the cells are 

 aggregated together in a compact layer at the surface. 

 Soon a straight line appears upon this layer, which is 

 called the primitive trace. This delicate line becomes 

 the basis for the spinal column ; and upon and about it 

 the whole individual is developed by an intricate proc- 

 ess of folding, dividing, and reduplication of the layer 

 of cells. One end of the line becomes the head, and 



