REPRODUCTION OF THE HYPOTRICHOUS INFUSORIA 49 



of monsters, the micronuclei were always present. The investi- 

 gations on this form, however, gave evidence that the hfe cycle 

 was essentially a limited one but that various chemical stimuli 

 could be substituted for conjugation to 'rejuvenate' the animals 

 and in this way the life history could be prolonged to a great de- 

 gree. Eventually, however, the organisms reached a stage where 

 it was found impossible to stimulate them further and the cultures 

 died out. 



Work by Woodruff ('05) on a number of the hypotrichous in- 

 fusoria, Popoff ('07) on the Stylonychia mytilus, and Gregory 

 ('09)on Tillina magna all gave additional support to the view that 

 the life cycle of these forms is a limited one. Both Woodruff and 

 Gregory were able to prolong the life of the cultures somewhat by 

 artificial stimulation. 



Enriques ('05) from his investigations on a number of spe- 

 cies of the Infusoria, including S. pustulata, came to the conclu- 

 sion that the degeneration which he observed in some cases was not 

 a so-called senile degeneration due to ' protoplasmic ' old age but 

 a degeneration caused by the toxic influences of certain bacterial 

 poisons in the culture media. 



Recent investigations by Woodruff ('08, '12) with Paramaecium 

 aurelia which he has kept on a ' varied environment 'medium^ have 

 shown that this organism can be bred indefinitely without conju- 

 gation or artificial stimulation, thus furnishing conclusive evi- 

 dence of the unlimited power of reproduction of an infusorian 

 without the need of 'rejuvenesence' when suitable culture condi- 

 tions are supplied. 



Jennings ('10), also working with Paramaecium, found no evi- 

 dence to support Maupas' view of the infertility of conjugation 

 occurring between closely related gametes. 



^ Woodruff ('08) thus described the 'varied environment' medium: "It was 

 found that Paramaecium can exist in nearly any infusion which may be made from 

 materials collected in ponds and swamps, and accordingly, in the hope of supplying 

 as far as possible all the elements which may be encountered in the usual habitat of 

 the organism, water was taken from ponds, laboratory aquaria, etc., together with 

 its animal and plant life. In other words, no definite method was employed in se- 

 lecting the material, but it was simply collected at random from many sources, 

 thoroughly boiled, and then used." 



