Origin of Sexuality 257 



Not only so, it is true that, whether we deal with passive or with 

 motile cells, these usually seek for and unite with some definite 

 portion of each conjugating individual. This strongly suggests 

 that powerful and very exact lines of energy act along the 

 conjugating or gamete substance of each. Thus in swarm- 

 spores the pointed, ciliate, and at times "eye-spot" end is 

 that where attraction-contact is first made. So, when the 

 eye-spot or similar mass is lateral or sublateral, fusion in like 

 position is made, wliile in Leptosira — already referred to — 

 attraction and union occur at the rounded posterior end, toward 

 which the eye-spot is nearest. What relation such union 

 bears to the position of the cell-nucleus has not yet been de- 

 termined. 



In the desmids a like exact line of attraction and union of 

 the passive sex-cells is observed. But the multicellular con- 

 jugate genus Spirogyra is most informing. When the annual 

 period for conjugation comes round — and this is often extremely 

 exact according to environal conditions — some filaments be- 

 come wholly giving filaments, others wholly receiving. Though 

 numerous efforts have been made to establish a chemical dif- 

 ference between these, it is doubtful if any sure result has been 

 reached; in fact we would interpret it in a different manner. 

 But in such species as S. maxima and S. nitiday though not 

 apparently in *S. longata, striking nuclear interactions occur 

 between the cells of sexually different threads. Thus the 

 "v\Titer pointed out in 1884 {101) that, even in such filaments 

 as have not yet conjugated, the commencing swellings of 

 opposite cells are put out in a direct line ^dth the nuclei of 

 each, no matter whether these are exactly opposite, or at vary- 

 ing oblique positions to each other. Again, if a cell in one 

 filament is slightly nearer to an opposite cell than to another 

 in that filament, a stronger and feebler tube may be formed 

 in the first; while, if it is exactly opposite the septum between 

 two cells, it may form two equal but oblique tubes to meet one 

 from each attracted cell opposite. Now all such tubes are 

 developed in exact line with the cell nuclei, and are not mere 

 haphazard growths of the wall under the molding influence 

 of the protoplasm alone. Overton and others have since 

 recorded like phenomena. 



So here at least it can be said that the nuclear chromatin 

 of the future conjugating cells is traversed by lines of force 



9 



