252 



BIOLOGY OF THE PROTOZOA 



of this reorganization process which they called "endomixis" was 

 the culmination of Woodruff's brilliant and long-continued study 

 of the life history of Paramecium aurelia which he began in 1907, 

 and which had been generally hailed as giving positive proof of 

 the correctness of Weismann's point of view. Parthogenesis, how- 

 ever, has the same effect upon organization and upon vitality 

 that conjugation has, and as Woodruff and Erdmann showed that 

 "endomixis" occurs approximately once in thirty days in Para- 

 mecium aurelia and about once in sixty days in Paramecium cau- 

 datum, any experiments and observations on vitality are valuable 

 only as they lie within these limits of time. For this reason many 

 of the conclusions of Hertwig (1889), of Joukowsky (1898), of 

 Calkins (1903, 1904, 1913) and of Jennings (1909, 1913) drawn from 



4.0 

 3.5 

 o.O 

 2.5 

 2.0 

 1.5 

 1.0 

 .5 

 



Fig. 133.— Vitality graph of Spathidium spathula. (After Woodruff and Spencer.) 



observations on Paramecium are of questionable value, and should 

 be used cautiously in connection with the present problem. In 

 other forms, however, analogous reorganization processes occur 

 during encystment and are thus advertized in cultures whereas 

 Paramecium does not encyst under such conditions but continues 

 with low vitality to live and move during such periods of depression 

 when "endomixis" is taking place. 



While the list of recent experimenters with the Infusoria is rather 

 a long one, the actual number of different organisms studied is 

 comparatively small, but different experimenters working with the 

 same species obtained strikingly similar results. Thus Pleurotricha 

 lanceolata has been studied by Joukowsky (1898) and by Woodruff 

 (1906), the former following out four series, three of which died out 

 after approximately 220, 250 and -142 generations without conjuga- 



