SEX-DETERMINATION IN ASPLANCHN^ 235 



mass cultures point to the following general conclusions: First, 

 all lines, if not all individuals of the species, possess the inherent 

 potentiality of male production, but whether this potentiality 

 shall lead to actual male production or remain latent depends 

 upon external conditions. Second, successful high feeding of the 

 humped type results in an increase of male production. Third, 

 continuous low feeding or starvation results in the parthenogenetic 

 production of females only. Fourth, sudden starvation of cul- 

 tures possessing a low metabolic level also results in pure par- 

 thenogenetic production of females and may even cause a reversion 

 from the more sexual or humped form of the Asplanchna to the 

 saccate or more purely asexual form. Fifth, slight starvation 

 of the well fed cultures may result in male production. 



To test the correctness of these tentative conclusions from mass 

 cultures, we turn to the task of definitely controlled experiments 

 with individual or isolation cultures. 



MALE PRODUCTION OF INDIVIDUALS UNDER HIGH NUTRITION 



From cultures of Series D (1910-11), were isolated fifty newly 

 born humped individuals, each of which was placed in an indi- 

 vidual culture abundantly supplied with Paramecia. Twelve of 

 the fifty, or 24 per cent became male producers (table 3). This 

 is about an average percentage, no more at least, than is shown 

 in the usual pedigree series of humped individuals. 



MALE PRODUCTION OF INDIVIDUALS STARVED IMMEDIATELY AT 



BIRTH 



During a period of six weeks, thirty-eight individuals were 

 isolated, within one hour after birth, from the general pedigree 

 series. The period of time during which the isolations were made 

 insured the elimination of accidental external factors. Each in- 

 dividual was examined under the microscope to be sure that no 

 food had been ingested and that no resultant development of 

 ovarian cells had taken place. All were placed in filtered cul- 

 ture medium. To four of these cultures food was added to con- 

 stitute special controls, although besides these there were the 



