XII.] CONJUGATION AND SEXUAL REPRODUCTION. I37 



the case, or the two successive 'reducing divisions' would lessen 

 the total number of ids, in each germ-cell, to one quarter. Two 

 idants are the normal number in Ascaris in. univalens, and they 

 are increased to four, by longitudinal fission : a single idant is 

 contained in each mature spermatozoon or ovum which is 

 formed by the two successive 'reducing divisions.' Hence 



JJkz llkz Tkz Kz, 



A 



^ 



A 

 i_ 



uv 

 o 



z 



B 



CI h 



gk 



o ^ ^ 



(h b r 



Fig. III. 



Diagram showing the behaviour of the idants in the various stages of 

 the development of the germ-cells in Ascaris megalocephala, var. univalens. 



A shows the actual behaviour of the idants, the final result {IV) of 

 which is a halving of the number of ids present in the first stage (/). 

 B shows that the arrangement of ids as a double row within the idants 

 would cause the final number ilV) to be a quarter of that present in the 

 first stage (7). Each of the four groups of figures in both^ and 5 repre- 

 sents the idants of a single cell of the corresponding stage. 



these mature germ-cells must contain half the total number of 

 ids contained in the two idants of the original germ-cell. If 

 this be so it is clear that the ids in the mother-idants are 

 doubled in number by longitudinal fission. The small letters 

 «, ^, c, &c. in the diagrammatic figure III, represent the ids 

 which compose the idants. The numbers I-IV. represent the 

 idants of each of the four stages,— the primitive germ-cells, 



