404 EDMUND B. WILSON 



(Diptera), that no doubt can exist of the widespread tendency of 

 the chromosomes to assume this arrangement already in the dip- 

 loid nuclei. It appears to me however that those authors who 

 consider the paired grouping to be a general characteristic of the 

 diploid nuclei go much too far.^^ Not only are numerous excep- 

 tions seen in the case of individual chromosome-pairs, but in many 

 cases no trace of paired grouping appears. Such exceptions may 

 readily be seen in the figures of Montgomery, Stevens, Morrill 

 and myself of the Hemiptera, which are probably unsurpassed 

 among animals for the clearness with which the size-relations 

 are shown. In cases where certain pairs may be unmistakably 

 recognized (as in Protenor and other Coreidea) the two members 

 frequently show no constancy of relative position — compare for 

 instance the accurate figures of the diploid groups of Protenor, 

 Anasa, Alydus and Nezara in my third 'Study' ('06) or those of 

 Morrill ('10) of Archimerus, Chelinidea, Anasa and Protenor. 

 But this does not in the least lessen the significance of the 

 remarkable cases that have been established. The tendency 

 towards such an association of the chromosomes in pairs is un- 

 doubtedly widespread; and the very fact that it does not follow 

 a fixed order may be used as an argument in favor of a conjugation 

 at the synaptic period. When the pairing is already evident in 

 the diploid groups the way for synapsis has been prepared in 

 advance. This process must take place at some time subsequent 

 to the association of the germ-nuclei in fertilization; and that 

 such a process undoubtedly occurs nullifies all the a priori 

 objections that might be urged against the possibility of a cor- 

 responding process that is delayed until the maturation-period 

 is reached. 



18 Strasburger, for example, says, "Ich zweifle nicht im geringsten daran, dass 

 es eich um eine allgemeine Erscheinung in diploiden Kernen dabei handelt, wenn 

 sie auch nicht immer auffallig ist" ('09, p. 90). Gates is still more specific. "It 

 is evident that the pairing of the chromosomes is not brought about at synapsis or 

 at any other period of meiosis, but that the chromosomes are really paired through- 

 out the life cycle of the sporophyte . . . Synapsis plays no special part in the 

 pairing . . . Meiosis and reduction consists essentially in the segregation of 

 the members of these pairs that have been in association since soon after fertili- 

 zation" ('11, pp. 334, 335). 



