XII.] CONJUGATION AND SEXUAL REPRODUCTION, l :; r, 



idioplasmic construction of the two daughter-nuclei must be 

 different. 



Inasmuch as we cannot see whether the chromatin granules 

 are made up of similar or different idioplasm, it follows 

 that direct observation cannot conclusively settle whether we 

 are dealing with an ' equal ' or a ' reducing division.' Perhaps, 

 however, we may succeed in decisively answering the question 

 by other means, and investigations have already been under- 

 taken with this special object ; for the present we must rest 

 content with conclusions based upon probability. Before 

 everything we must make certain that the first division in 

 eggs requiring fertilization is, in all cases, a ' reducing division.' 

 At the present time Artemia reproduces sexually in many of 

 its colonies, and hence in parthenogenetic colonies in which 

 the eggs have lost the second polar division but have retained 

 the first, it may be regarded as probable that the latter has 

 kept its original form, i. e. that of a ' reducing division.' 



Still further support for the above conclusions is found hi 

 the fact that Dr. vom Rath could never find single idants in 

 the equatorial plate of the polar spindle of Artemia, but only 

 double ones, each having the form of two large round bodies 

 lying over each other (Fig. IX. 3 a). 



If we now further consider that, at the commencement of 

 the change of the germinal vesicle into the spindle, the 

 chromatin granules lie scattered through the whole thickness 

 of the former (Fig. IX. i), and that they then fuse with one 

 another, arranging themselves as a single layer in the equa- 

 torial plane of the spindle, in the form of an oval disc and not 

 that of a simple wreath (Fig. IX. 2), and if we remember that 

 they then pass into the arrangement of a double wreath (Fig. 

 IX. 3 a), we are led to conclude that no two idants of this 

 double wreath have arisen from the doubling by division of 

 a single idant, as is the case in the usual ' equal division ' ; 

 but that the idants of the oval equatorial plate, which arose 

 independently of one another, have subsequently come to place 

 themselves one upon the other in the form of a double wreatli. 

 If this conclusion be sound we have to do with a true 'reducing 

 division.' 



Hence we are justified in assuming as the most probable 

 conclusion that a 'reducing division ' takes place, and further- 



