REPRODUCTION 



B. CONJUGATION. 



Conjugation, which means the union of two separate 

 individuals for the purpose of propagation, gives us the 

 true connecting-link between asexual and sexual repro- 

 duction. The transition between them is very gradual so 

 much so that we may trace every stage from the union of 

 two organisms completely alike in every respect up to the 



CK 



FIG. 10. CONJUGATION OF ^'OCTILUCA. (After Ischikawa.) 

 (From Weismann, " The Evolution Theory.") 



A, two individuals coalescing; B, fusion of cells ; C, beginning of 

 division ; D, completion of division ; pr, protoplasm ; K, nucleus ; 

 G, cell-body ; CK, centrosome. 



true sexual mating of distinct male and female in the 

 higher animals. 



We have, to begin with, two (or rarely more) individuals 

 of the species (as in Algae or Infusorians) simply mingling 

 their combined bodies into one, and thereafter multiplying 

 by simple division in the ordinary manner. In the Bell- 

 animalcule ( Vorticella) , mentioned once before, conjugation 

 takes place between the large mother-animal and one of 

 the much smaller progeny, which has resulted from re- 



3 



