232 CLAUDE W. MITCHELL 



WELL FED MASS CULTURES OF THE HUMPED TYPE 



To twenty mass cultures derived as were the preceding, food — 

 chiefly Paramecia — was supphed in sufficient quantity to ensure 

 abundance for each individual. The humped type was main- 

 tained in these cultures and in every one of the twenty males 

 were produced at some time during the three weeks they were 

 continued. Yet male production was by no means simultaneous 

 or uniform in amount; in but one culture did the number of 

 males at any one time become noticeably great, this toward the 

 end of the period. It is difficult and perhaps impossible to in- 

 terpret these minor, though striking differences. They could not 

 be referred to variations in conditions surrounding the cultures; 

 but within a mass culture cannibalism or many other unobservable 

 incidents may take place which complicate results. It is plain 

 however, that the results of this experiment, indicate a greater 

 tendency toward male production in well fed mass cultures than 

 in those poorly fed or starved. This result stands in evident 

 contradiction to statements of workers upon Hydatina senta, al- 

 though a careful reading of Nussbaum's experiments suggest the 

 possibility of a like interpretation. 



INFLUENCE OF CULTURE MEDIA UPON MALE PRODUCTION 



To test the possible effect upon male production, of metabolic 

 products or other substances in solution, the entire culture me- 

 dium was filtered from the mass culture mentioned above in which 

 an unusual number of males had appeared. This filtrate was 

 added unsparingly to a mass culture of the humped type in 

 which as yet no males had been produced. The results were 

 wholly negative and indicated, in so far as one experiment is of 

 value, the improbability of the culture medium containing the sex- 

 determining factor. We will merely add that extensive observa- 

 tion in regard to various media and especially in regard to older 

 mass cultures seem to negative the probability of any direct in- 

 fluence of dissolved matter upon male production. It has been 

 repeatedly observed that male production in this rotifer is fre- 

 quent and copious in the most diverse fluid-media and even in 

 the heaviest compost filtrate. 



