LIFE CYCLE OK SIMOCEPHALUS VKTULUS. 87 



having practically ceased. Another culture was established 

 from this by selecting a tVw specimens at random and giving 

 them a fresh supply of algae. It ran through a similar period of 

 great productivity, about the same number of sexual forms occurr- 

 ing, and declined as in the first instance. A third fresh culture 

 was stocked by a single specimen from the last. It likewise gave 

 rise to a great profusion of Daphnians, sexual forms appearing 

 in considerable numbers. Unfortunately I did not keep a record 

 of the time it took in the last two instances for the sexual forms 

 to appear; but, as shown above, the first culture, started August 

 i, produced 50 ephippial eggs by August 13, and that in the 

 presence of an enormous quantity of green alga?, the container 

 being a three gallon jar which had previously been used for 

 Paramecia. This Paramecium culture had been started with 

 boiled wheat as the source of nutrition and had been permitted 

 to stand for nearly a year. The Paramecia had disappeared and 

 green alga2 had developed in immense quantities on the side of 

 the jar away from the light. Dearth of food could not have been 

 a factor in inducing sexuality in this culture. I have already 

 shown in isolation experiment 2 that sexuality comes on in spite 

 of an abundance of food, in small vessels containing only a single 

 individual female. The study of general cultures leads to con- 

 clusions whjch are in agreement with results obtained by a study 

 of isolated females, namely, that onset of sexuality is independent 

 of food shortage, and suggests that it is related to accumulations 

 of certain excretions, which become critical in their effect upon 

 the kind of offspring surprisingly early in Simocephalus cultures 

 which are allowed to run their natural course unhindered. 

 Production of ephippial eggs reaches its highest level about t he- 

 time a general culture is over stocked and tin- rate of reproduction 

 has begun to decrease, passing to lower levels as the food supply 

 decreases, as is readily demonstrable it" one will but take the 

 trouble to remove them as' they appear in such a culture, record- 

 ing the daily output. 



Of all the females isolated for study and kept in small containers 

 in the laboratory, including several hundred selected at random 

 and as many more whose pedigree was known for several genera- 

 tions, also 60 stem mothers and all of their female offspring that 



