The Evidence from Hybrids. 125 



it requires that each sexual element should contain gem- 

 mules from every part of the body of the parent, it is 

 directly opposed to any such result, and there is no 

 place for it in any other hypothesis of heredity. Our 

 theory fits it exactly, however, and a more crucial test 

 could hardly be proposed than an experiment like those 

 detailed by Gartner. 



Reciprocal Hybrids. 



According to Darwin the two sexes play similar parts 

 in heredity, and any characteristic whatever may be 

 transmitted by either sexual element. 



This conclusion is based upon the phenomena of cross- 

 ing, but a little thought will show that it is impossible, 

 from the nature of the case, to prove it from evidence 

 of this kind, although, as I hope to show, it is capable 

 of disproof. 



Only animals of the same species, or of closely related 

 species, can breed together. Closely allied animals are 

 alike in all respects, except as regards the slight differ- 

 ences which distinguish species, varieties and individu- 

 als from each other. Since no animals or plants can 

 cross except those which have most of their past history 

 in common, and which are therefore alike in nearly 

 every respect, it is plainly impossible to prove, from the 

 phenomena of crossing, that each parent has power to 

 transmit the features which are shared by the other par- 

 ent as well. The phenomena of parthenogenesis, or re- 

 production by virgin females, as in the case of bees and 

 wasps, show that the ovum alone may transmit all the 

 established hereditary structure of the species, but there 

 is and can be no evidence to show that the male element 

 can accomplish the same thing. 



The facts of crossing, while they cannot prove that the 



