THE WAY LIFE BEGINS 55 



is desirable, therefore, that a clear idea of the whole of the 

 reproductive structures be obtained, and especially of the 

 really important ones, the ovary and testis. 



The testes of many mammals and of man are found sus- 

 pended on the outside of the body near the outlet of the 

 spermatic tube. (In the rabbit, the subject of our study, the 

 testes are not on the outside of the body except at the breed- 

 ing season.) The location of the testes in this region apparently 

 disproves the assertion that the male and female structures 

 correspond. But the testes of the male of mammals and of 

 man are found in the embryo, long before birth, in the same 

 position as that occupied by the ovaries of the female, namely, 

 back of the kidneys. Before birth there is a 'descent' or 

 migration of the testes from their original place to the scrotal 

 sac outside. Evidence of the change of position of the testes 

 is seen in the spermatic ducts, which very early in the life of 

 the embryo connect the testes with the penis, but later 

 lengthen their tubes and follow the testes to their new posi- 

 tion. They therefore form loops in front of and on each side 

 of the bladder in passing from the testes to the neighboring 

 outlet (Figure 6, page 63). 



The eggs and the sperm cells of the rabbit share the lower 

 portion of the canal leading to the outside with another 

 product of the body, that from the kidneys. The kidneys 

 empty their secretions into the bladder and the latter empties 

 into the vestibule, not far from the outer end of the tube. 



The History of a Fertilized Egg 



At intervals, six or more small, naked eggs are discharged 

 by the ovaries into the expanded end of the oviduct. On 

 the way down the oviduct they may be met and fertilized by 

 sperm cells from the male. If so, they immediately begin to 

 develop, and by the time they reach the uterus have already 

 thrown out finger-like processes which enter the walls of the 

 uterus. Through these, oxygen and nourishment are drawn 

 from the mother. The five or six eggs have taken up positions 

 in the uterus, and here, as they grow, become surrounded 

 by two envelops, each forming a sac, the inner one of which 



