302 THE CELL 



Falkenberg concludes from his observations, that the attraction 

 between the ova and spermatozoids of Cutleria makes itself felt at 

 a relatively great distance, that this attractive force must have its 

 seat in the cells themselves, and further that the attraction is only 

 exerted between sexual cells of the same species. 



De Bary (VII. 2 b), investigating the sexual reproduction of 

 Peronosporess, observed that, in the interlacing hyphse, the oogonia 

 at first lie alongside of each other. Somewhat later, the anther- 

 idia develop, but this invariably occurs in the immediate neigh- 

 bourhood of the egg-cell only ; they are frequently derived from 

 hyphse, which have no connection with the one from which the 

 oogonium is formed. De Bary concludes from this, that the 

 oogonium must exert an influence over a limited area, and that 

 this influence induces the hyphae to form an antheridium. A 

 peculiarly striking instance of this influence exerted at a distance 

 is seen in the circumstance, that the branch on which the an- 

 theridium is developed is diverted from its natural direction of 

 growth ; for, in order to approach the oogonium, it bends over with 

 its end towards it, and then lies close to it. De Bary estimates 

 that the distance at which the oogonium is able to exert this 

 attraction is almost as great as its own diameter, and remarks 

 further, that " the above-described divergence of the lateral 

 branches can be ascribed to no other cause than the special 

 attributes of the oogonium." 



Not less interesting, and worthy of notice, are the statements 

 which Engelmann (VII. 9) has made about the conjugation of 

 Vorticella microstoma. In this case small male zoospores are 

 formed by budding (p. 228) ; these, just like spermatozoa, fertilise 

 the large female individuals (p. 271). Engelmann succeeded four 

 times in tracing the bud after its separation from the mother-cell, 

 until it had united with another individual. 



Engelmann describes his observations as follows : " At first the 

 bud, always rotating on its longitudinal axis, wandered with fairly 

 constant rapidity (cir. '6-'l mm. per sec.), and, as a rule, in a fairly 

 straight line through the drop. This lasted for from five to ten 

 minutes, or even longer, without anything especial happening ; 

 then the scene was suddenly changed. Coming by chance into the 

 neighbourhood of an attached Vorticella, the bud changed its 

 direction, occasionally even with a jerk, and dancing, like a butter- 

 fly which plays round a flower, approached the fixed form ; it then, 

 as if it were feeling it, glided round about it, meanwhile always 



