STATISTICS OF MULTIPLE BIRTHS 



21 



6 PROCESSES IN THE DETERMINATION OF SEX SUGGESTED BY 

 THE STATISTICS OF MULTIPLE BIRTHS. 



The view that, if the sex is not completely determined in the original 

 formation of a germ, it must be determined at some definite moment of 

 development that there can be no intermediate state between complete 

 asexuality and complete sexuality is one which, at first sight, seems 

 almost axiomatic. And yet, the preceding statistics of multiple births 

 seem to show that such is not the case, and that there may be a series of 

 causes acting first in one direction and then in the other, each of which 

 tends to make one sex or the other more probable until, gradually, the 

 sex is definitely determined. An analogue to this determination by a suc- 

 cession of accidental causes may be constructed in the following way: 

 Let A be a large pipe or aqueduct, from the mouth B of which a stream 

 flows into a gradually widening river V. At a certain distance below 





the exit B the river is divided into two branches by a promontory P. On 

 one side of this promontory, which we may call the male side, the river 

 is slightly broader than on the other. Between the exit and the promon- 

 tory, the river flows over a rough bottom with many eddies, but the ulti- 

 mate result must be that every drop of water which conies from the 

 conduit ultimately passes on one side of the promontory or the other. 

 But the side on which it shall pass is not determined at any one moment, 

 As a drop, or, to give the analogy a more complete form, a small particle 

 suspended in the water, leaves the conduit, it is equally likely to pass into 

 one branch of the river or the other. If it chance to incline to the right 

 after leaving the conduit, there will be a greater probability of its passing 

 into the right branch, but this will be only a probability until a certain 

 point of the course is reached. A particle reaching the point M, for 

 example, will be likely to go into the female branch, but yet may be car- 

 ried by an eddy across to the opposite side before it reaches it. One at 

 N, although farther down, will still be uncertain ; possibly its course may 

 not be decided until it almost reaches P. A particle on one bank or the 

 other will be more and more likely to pass into the corresponding branch 

 the farther down it is found. When the particle once crosses one of the 

 dotted lines PPi and PS the branch it will take will be completely deter- 

 mined. 



