HEREDITY 227 



animals may not copulate. But where the fertilization of the ova 

 may be a quite promiscuous affair there may still be infertility 

 between individuals belonging to different species. Thus the 

 eggs and spermatozoa of cod, haddock and whiting may be 

 spawned into the same restricted part of the sea and fertilization 

 may occur in the water and outside the bodies of the parent- 

 animals. We might expect, in such a case, that the sperms of, 

 say, cod, would sometimes fertilize the ova of whiting, but 

 undoubted hybrids between these and other species of Teleostean 

 fish that reproduce in this way are practically unknown. It is 

 also known that artificial impregnation of the ova of one kind of 

 fish by the spermatozoa of another kind may result in the 

 segmentation of the ovum, but rarely in a developmental process 

 that proceeds so far as the hatching-out of the embryo. Therefore 

 there must be physiological reasons for the infertility. 



If no offspring results from the crossing of individuals belonging 

 to different categories we say that these crossings are immediately 

 sterile. If hybrid offspring do result from such crossings and if 

 these hybrids are sterile animals we say that the original crossings 

 are ultimately sterile. If the hybrids are fertile with each other 

 for a number of generations but if the strain tends to die out 

 there is again ultimate sterility. The matter may be very com- 

 plicated : thus European men are fertile with Negro w^omen and 

 the mulattoes and mulattresses so produced are fertile with each 

 other and with individuals belonging to the parent (European 

 and Negro) races. But the mulattress crossed with the mulatto 

 is said to have few children and to abort easily so that this strain 

 tends to die out, the crossing, mulatto X mulattress, being 

 ultimately sterile. On the other hand, the mulatto and mulattress 

 when crossed with individuals of either of the parent races are 

 immediately and ultimately fertile, for the strain persists, though 

 it tends continually towards a parental racial strain. When the 

 original Dutch colonists settled in Java a race of hybrids (with 

 the native women) came into existence. These '' Lipplappen " 

 are said to have been immediately fertile with each other, but such 

 crossings resulted in the births of girls only and these girls were 

 sterile. Therefore the original crossings were ultimately sterile. 



796. The Sign of the Crossing. It matters which way the 

 cross is made : male A X female B is not the same thing 2i?, female B 

 X male A [A and B being different categories). Thus the cross 



