120 CLAUDE W. MITCHELL 



Production of the third or campanulate type of Asplanchna amphora 



Although not previously mentioned except in the case of the 

 last culture, we need to add that the third or campanulate type of 

 the A. amphora appeared in a number of the mass cultures. Ex- 

 amination of their stomach contents showed then to be cannibals. 

 They reproduced either their own type, males, or the humped 

 type, using young of their own species as food. Pedigree experi- 

 ments were begun with this type; however, the delicacy of the 

 feeding technique and the amount of time required caused us to 

 abandon them after five generations. 



Male production 



In view of the unsettled question of sex determination and of 

 the light which our experiments might throw upon it, careful 

 records were kept in all pedigree lines and mass cultures of the 

 male production, but a full discussion of the data thus obtained 

 is left for another paper in the course of preparation. Never- 

 theless we may well add the interesting facts that males are rarel}^ 

 produced by the saccate form of the species, throughout however 

 many generations it is cultivated. On the other hand, they are 

 frequently produced by both the humped and campanulate types. 

 There is an undoubted difference in physiological level which is 

 registered by the transition from one of these forms to another 

 and this furnishes a new and valuable instrument for attacking the 

 problem of sex determination, work upon which is now under way. 



DISCUSSION OF GENERAL RESULTS 



One general and striking result in the foregoing experiments 

 is the relative stability under many conditions of the smaller 

 saccate A. amphora. Instead of being a transient developmental 

 form all but inevitably giving place to the humped rotifer within 

 a few generations, the experiments point strongly toward the 

 conclusion that this form may propagate itself indefinitely with- 

 out marked morphological change. The greater stability of this 

 form adds to the interest of the phenomena as not unrelated to 



