514 BIOLOGY OF THE PROTOZOA 



indicate that environmental stimuli are without effect in producing 

 conjugations unless the protoplasm is in a condition where such 

 conjugations are possible. Indeed, when fidly mature, i. e., 

 when the protoplasmic conditions are just right for conjugation, 

 union will take place in a rich food medium and without the tran- 

 sition from full nourishment to hunger. This phenomenon is 

 abundantly illustrated in the records of Uroleptus viobilis and in 

 my records of Paramecimn caudutum, BlejjJuirisma iindvlans, or 

 of Dldinium nasutuin. There is little information as to the exact 

 nature of these protoplasmic conditions prior to conjugation, 

 Zweibaum (1922) gives good evidence to show that the quantity 

 of glj'cogen in the cell is reduced to a minimum at this period, the 

 large drops of neutral fat disappear while small droplets of another 

 type make their appearance together with sfsme cholesterine ester 

 and large quantities of what was interpreted as fatty acids. These 

 are probably effects of inadequate food material, for the observer 

 obtained similar results with Paramecia under conditions of starva- 

 tion which were not followetl by conjugation. 



II. INTERNAL CONDITIONS AT THE PERIOD OF FERTILIZATION. 



In the last analysis both internal and external conditions play 

 their respective parts in protoplasmic preparations for conjugation. 

 Without external stimuli, without oxygen and food, vitality would 

 soon cease; with them, vitality manifested by metabolism and 

 reproduction will continue. With metabolism, however, the pro- 

 toplasmic make-up is constantly changing and these changes are 

 shown by the general reactions and by the organization (see Chapter 

 IV). According to Hertwig, 1908, Popoff (1908), and Rautmann 

 (1909), the changes thus brought about lead to disturbances of the 

 normal ratio of nucleus to cytoplasm (Kernplasmaverhaltnis) 

 and lead to conjugations whereby the normal relation of nucleus 

 to cytoplasm is regained. Whatever the changes due to metabolism 

 are in a given case the conclusion is forced upon us by the mass of 

 evidence that given external conditions will provoke conjugations 

 at one period of the life cycle and will have no effect in producing 

 them at another period, while at the critical period of maturity 

 external conditions may be entirely negligible as they appear to be 

 in the Coccidiomorpha and in gamete-forming organisms generally. 

 Here protoplasmic and not external conditions control the issue. 

 There is some significance in the fact that encystment (with endo- 

 mixis) is induced by the same external conditions as is conjugation. 

 Mengheni (1913) found that Stylonycliia will not encyst if food is 

 abundant but that hunger and low temperature are necessary con- 

 ditions. With Uroleptus mohilis conjugation and encystment tests 



