PHENOMENA ACCOMPANYING FERTILIZATION 511 



tion tests are made at regular intervals in all complete isolation 

 culture work. Such tests have been made with Vrole'ptiis mohilis 

 e\'ery ten to fifteen days. 



The usual interpretation of this result is not very enlightening; 

 it runs somewhat as follows: After abundant feeding and active 

 division the large numbers of individuals produced soon exhaust 

 the food, and hunger follows; conditions thus due to hunger result 

 in conjugations provided the organisms are mature. Jennings 

 (1910) qualified this general statement by emphasizing the necessity 

 of a preliminary period of active multiplication in a rich food 

 medium. "The cause of conjugation" he states, "is a decline in 

 the nutritive conditions after a period of exceptional richness that 

 has induced rapid growth and multiplication" (loc. cit. p. 292). 

 All experimenters since Maupas have used this method with more 

 or less success and it appears to be empirically sound. Some 

 observers however, interpret the phenomenon as due exclusively 

 to such purely environmental conditions. Thus Chatton (1921) 

 argues that inanition is indeed an "internal condition" but the lack 

 of food which causes it is an external factor. "Inanition" he says, 

 "is a condition which is practically all that is needed for conjuga- 

 tion; it is an almost certain means of obtaining conjugations in no 

 matter what wild culture, and })ecomes the chosen technical means 

 of producing them. In current theories, however, conjugation is 

 regarded as independent of the external conditions, inanition playing 

 only an occasional role" (loc. cit. 131). Yet, in a footnote (page 

 135), Chatton Aery properly calls attention to the fact that condi- 

 tions which call forth conjugations in nature do not cease after 

 conjugation is ended. Indeed it is an unwarranted assumption to 

 explain conjugations in nature as induced by a period of rich feeding 

 followed by a period of lack of food, and this in turn replaced by a 

 rich nutrient medium useful to the ex-con jugant. To this extent 

 the method employed in the laboratory to obtain conjugating 

 pairs is entirely artificial. Chatton's reflections and conclusions 

 supporting the view that external conditions are alone responsible 

 for conjugation are included in his excellent description of the struc- 

 tures, division, and conjugation of parasitic ciliates of the family 

 Nicollellidce, particularly Nicollella and CoIlineUa. In the former 

 the conjugating individuals measure approximately one-fifth of the 

 vegetative forms; in the latter approximately one-half, in both types 

 the conjugating individuals differ in morphological details from the 

 vegetative forms. He interprets these changes as due to the 

 particular part of the digestive tract to which the parasites are 

 carried. Chatton's perplexity and call for further experimental 

 evidence in solving the raisnn d'etre of conjugation is justified and 

 the problem will probably remain ])erplexing so long as external 

 conditions alone, are regarded as the controlling factors. 



