XII.] CONJUGATION AND SEXUAL REPRODUCTION. 1 43 



the idant, the longitudinal splitting of the latter certainly in- 

 volves an 'equal division.' It appears doubtful, however, 

 whether this arrangement is universally present, and I should 

 be incHned to question its existence in the second division of 

 the mother-cells of Pyrrhocoris, and to believe, on the other 

 hand, that the ids are arranged in two rows, and that the idant is in 

 reality double. This arrangement w^ould then lead to a new and 

 different type of reducing division.' If the letters a be, &c.—m. 

 in Fig. V, represent the ids, and the vertical line drawn through 

 A, the plane of splitting, it is clear that division of the idant 

 would result in a reduction of the total number of ids to half in 

 each of the daughter-nuclei, as is shown in B. 



Fig. V. 



A. One of the double idants from the equatorial plate of the nuclear 

 spindle of the first ' reducing division.' B. The same, showing its 

 position after the occurrence of the first ' reducing division ' in the equa- 

 torial plate of the nuclear spindle of the second ' reducing division.' 

 (Compare Fig. IV. 5 and 6.) 



In support of this assumption there is not only the impossi- 

 bility of conceiving the universal occurrence of a second 

 division which is not also an essential change in the nuclear 

 substance, but, as will be afterwards shown, there is in addition 

 the evidence derived from the figures of the process which 

 Henking has published. 



The equatorial plate of the nuclear spindle of the first ' re- 

 ducing division ' is composed of two sets of twelve idants 

 arranged in two wreaths opposite to each other (see Fig. IV. 5). 

 Twelve then pass to one and twelve to the other pole, com- 

 pleting the first ' reducing division.' Now it can be clearly 

 seen that each idant is double from the very first, consisting of 

 two halves which are arranged side by side in the spindle 



