342 HOYT S. HOPKINS 



more specific way, is not clear. Hypertonic solutions of 'tap- 

 water' or of glucose produce like results to a lesser degree, but 

 they act apparently by increasing the osmotic concentration of 

 the medium, so that their effect is probably not a specific one 

 in the chemical sense. The result produced by any one of these 

 reagents is to augment the intensity of conjugation (increase 

 the proportion of conjugating animals), for a small percentage 

 of individuals may conjugate in a culture to which water alone 

 has been added (in place of salt solution), or sometimes even in 

 the main culture which had been renewed with hay infusion. 



In the light of this recent work in which refined methods of 

 experimentation were employed successfully with one race, the 

 question has been asked whether we cannot by such means 

 induce conjugation in any race of infusoria. As applied to 

 Paramecium in particular — are there any racial differences in 

 respect to conjugation, or are the alleged diversities environ- 

 mental in origin? According to Zweibaum, we ought to be able 

 to induce conjugation in any race of Paramecium caudatum by 

 using those methods which he finds most effective, for he holds 

 that all supposed racial diversities, such as those described by 

 Jennings and Hargitt ('10) for size, result from cultural differ- 

 ences. To state his position more clearly, I quote from page 

 276 of his paper: 



Dernierement encore pour les Paramaecies Jennings determine di- 

 verses races — injustement a mon avis — et affirme que les conditions de 

 conjugaison different considerablement selon ces races. L'auteur 

 deplace ainsi le centre de gravity de la question sans ajouter une con- 

 ception nouvelle et un determinisme positif dans les considerations de 

 conjugaison chez les Paramaecies. 



And again, in summarizing the conditions which he considers 

 sufficient for conjugation in Par. caudatum, he writes (p. 292) : 



Comme conclusion nous pouvons dire que les Paramaecies que Jen- 

 nings et Hargitt croyent appartenir a des races diverses, se conjugueront 

 toujours, lorsque aprcs avoir passe par un etat de disette prolongee de 5-6 

 semaines, on rcmplira les autres conditions necessaires — a savoir — la 

 disette comme agent de Faction instantanee, la temperature de 20- 

 23°C. et la composition du milieu (voir 2c'me partie). 



Ce qu'on dit etre des races diverses de Paramaecium n'est que le 

 resultat de la quantite de la nourriture. 



