THE GENERAL SIGNIFICANCE OF AMPHIMIXIS 211 



_ Why, then, is there such an intimate, and in the case of the 

 higher types, snch an indissoKible, association between reproduction 

 and amphnnixis that ' fertilization ' appears to be a sine ^a non of 

 reproduction, and not very long- ago seemed to us to be the 'quicken- 



to^explodtr™' ^^' '^''™"'^' '^''^ ' ''^^"'^ '""'"' ^^'' powder-barrel 

 The reason of this is not difficult to discover; it lies in the 

 structure of multicellular animals, and in their differentiation accord- 

 ng to the principle of division of labour, for since only particular 

 e.l s are capable of reproduction, that is, of giving rise to the whole, 

 t IS m these necessarily that the process of amphimixis has to occur 

 It Its sigmhcance hes in its effects on the succeeding generations. It 

 IS true that m the lowest multicellular organisms, suc5 as the species 

 of Fote, there are, m addition to the sex-cells, other reproductive 

 ce Is quite similar to the ova, whose development into a new colony 

 tak^s place without amphimixis, but the higher we ascend in the 

 animal and plant senes the rarer are these 'asexual' germ-cells or 

 spores, and in the highest animal types they are entirely absent and 

 leproduction occurs only by means of the 'sex-cells ' 



I am inclined to look for the cause of this striking phenomenon 

 mainly n. he fact that, if amphimixis had to be retained, this was 

 eflected with mcreasmgly great difficulty the more highly and com- 

 p^xly differentiated the organisms became,and that mot. complicated 

 adaptations were therefore necessary in order that the union of the 

 two germ-cells might be rendered possible at all. There is first of 

 all the separation into two kinds of sex-cells, whose far-reaching 

 differentiations and precise adaptations to the most minute conditions 

 we have already discussed : then follow the innumerable adaptations 

 to bring about the meeting of the sex-cells, the arrangements for 

 opulation and, finally, the instincts which draw the two sexes 

 together, the means of attraction which are employed, whether 

 decorative colours or attractive shapes, stimulating odours or musical 

 notes, m short, all the diverse and intricate arrangements, which seem 



the ladder of life When we call to mind that sexual differentiations 

 finally go so far that they dominate the whole organism, alike in its 

 external appearance and in its internal nature, its feelings, inclinations 

 instincts, Its will and ability, as well as its structure^ down to the 

 finest nerve-elements, we can understand that a mode of reproduction 

 which demands such a composite disposition of details, involvino- 

 a moulding of the whole organism, so to speak, from birth till death 

 must of necessity remain the only one, and that there was no room 



