THE STRUGGLE FOR TUE LIFE OF OTHERS. 247 



on the same branch, yet so unlike one another in form 

 and color that the untrained eye would never know 

 them to be relatives. Even when male and female are 

 grown on the same flower-stalk and enclosed in a 

 common perianth, the hermaphroditism is generally 

 but apparent, owing to the physiological barriers of 

 heteromorphism and dichogamy. Sex-separation, in- 

 deed, is not only distinct among flowering plants, but 

 is kept up by a variety of complicated devices, and a 

 return to hermaphroditism is prevented by the most 

 elaborate precautions. 



When we turn to the animal kingdom again, the 

 same great contrast arrests us. Half a century ago, 

 when Balbiani described the male and female elements 

 in microscopic infusorians, his facts were all but 

 rejected by science. But further research has placed 

 it beyond all doubt that the beginnings of sex are 

 synchronous almost with those shadowings in of life. 

 From a state marked by a mere varying of the nuclear 

 elements, a state which might almost be described as 

 one antecedent to sex, the sex-distinction slowly 

 gathers definition, and passing through an infinite 

 variety of forms, and with countless shades of 

 emphasis, reaches at last the climax of separateness 

 which is observed among birds and mammals. Often, 

 even in the Metazoa, this separateness is outwardly 

 obscured, as in star-fishes and reptiles ; often it is 

 matter of common observation ; while sometimes it is 

 carried to such a pitch of specialization that only the 

 naturalist identifies the two wholly unlike creatures 

 as male and female. Through the whole wide field 

 of Nature then this gulf is fixed. Eacli page of the 

 million-leaved Book of Species must be as it were split 



