PART III 

 DEVELOPMENT AND LIFE-HISTORIES 



CHAPTER XIV 



THE CONTINUANCE OF LIFE 



1. Modes of reproduction 2. The evolution of sex 3. Divergent 

 modes of reproduction 4. Historical 5. The egg-cell or ovum 

 6. The male-cell or spermatozoon 7. Maturation 8. Fer- 

 tilisation. 



IN his exercitation " on the efficient cause of the chicken,' 5 

 Harvey (1651) confesses that " although it be a known 

 thing subscribed by all, that the foetus assumes its original 

 and birth from the male and female, and consequently 

 that the egge is produced by the cock and henne, and the 

 chicken out of the egge, yet neither the schools of 

 physicians nor Aristotle's discerning brain have disclosed 

 the manner how the cock and his seed doth mint and 

 coine the chicken out of the egge." The marvellous 

 facts of development are familiar the sprouting corn 

 and the opening flowers, the growth of the chick within 

 the egg and of the child within the womb ; yet so diffi- 

 cult is the task of inquiring wisely into this marvellous 

 renewal of life that we must reiterate the old confession : 

 " ingratissimum opus scribere ab iis quse, multis a natura 

 circumjectis tenebris velata, sensuum lucis inaccessa, 

 hominum agitantur opinionibus." 



1. Modes of Reproduction. The simplest animals 

 divide into two or into many parts, each of which becomes 

 a full-grown Protozoon,, There is no^ difficulty in under- 



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