The Lije-History of Hypotrichous Infusoria. 607 



light of Maupas's results with Oxytricha sp. and Stylonychia 

 mytilis, and of Joukowsky's with Pleurotricha lanceolata, and 

 also my own on two cultures of Oxytricha fallax, two of Pleuro- 

 tricha lanceolata and one of Gastrostyla steinii, it would seem to be 

 questionable whether conjugation is of so frequent occurrence 

 among the Hypotrichida as in some other groups of Ciliata. 



V. PHYSIOLOGICAL AND MORPHOLOGICAL VARIATION DURING THE 



LIFE-CYCLE. 



Maupas emphasized the fact that various changes, cytoplasmic 

 and nuclear, take place in Protozoa as "senile degeneration" 

 advances; and he also found physiological evidence in the form 

 of lessened vitality, increase of endogamous conjugation, and 

 infertile syzygies. Joukowsky found no morphological changes 

 in Paramoecium but observed that the rate of division decreased 

 as the cultures advanced and that many of the animals became 

 sluggish. In an eight month culture of Pleurotricha he found 

 no signs of degeneration. Simpson made some observations on 

 three to four month cultures of Stylonychia pustulata, Para- 

 mcEcium caudatum, and Paramoecium putrinum, and while he 

 did not find degeneration in such specific form as nuclear changes 

 or loss of external appendages, still he was "convinced of a gradual 

 ehbing of vital energy as the series proceeds, which expresses 

 itself in slower motion, in a tendency to inactivity and general 

 listlessness, if the word be admissible in this connection, as also in 

 a certain diminution of size that was not remedied by any amount 

 of food." Calkins ('04), however, found marked cytoplasmic and 

 nuclear changes in his long Paramoecium cultures, and physio- 

 logical degeneration was manifested by irregular and abnormal 

 divisions, decreased division-rate, tendency to endogamous con- 

 jugations, and above all by the "death of all members of a series 

 fed continually on the same diet of hay-infusion." 



/. Physiological Variation. 



In my cultures, physiological changes have been manifested 

 chiefly in the slowing down of the division-rate after a greater 

 or less number of generations, and coincident with this, in a con- 

 siderable lessening of the general activity of the infusorians. 



