MALE-PRODUCTION IN HYDATINA 159 



has taken place in growth or maturation, and her nature is no 

 longer subject to alteration. What happens to decide this 

 fate is unknown. It may be the failure of some chromosome 

 to divide. The male-producing female may haA^e fewer chromo- 

 somes than the female-producer. The apparent variability 

 of the number of chromosomes (Whitney, '09) may be due, not 

 entirely to difficulty in counting them, but partly to actual 

 differences. 



If such behavior of the chromosomes results in the develop- 

 ment of a male-producer, the rate of formation of the spindle, 

 or of the diAision of chromosomes, may be the cause of the 

 chromosome change. A chromosome dividing a Uttle later 

 than its fellows may be drawn (?) to one pole without completing 

 its division. The cytology of the germ cells of Hydatina should 

 be re-examined, with a view to discovering the difference be- 

 tween male-producing and female-producing females. But we 

 emphasize that our theory of the speed of reaction is not bound 

 up with chromosomes, to stand or fall with future discoveries 

 regarding the chromosomes of these rotifers. Other phenomena 

 than chromosomes which have, with present technique, no visible 

 expression, may as conceivably be influenced by the speed of 

 metabolic processes. 



If male-production is related to the rapidity with which cer- 

 tain physiological processes occur, it is not surprising that a 

 change of en\ironment more often reduces male-production 

 than increases it. A high degree of male-production, on our 

 view, depends upon an efficient mechanism working at top 

 speed. Any unskilled workman may ruin a delicate machine, 

 it takes an inventor to improve it. Many changes of en\dron- 

 ment may retard metabolic processes, only a few accelerate them. 

 We should expect, therefore, that most agents which affect the 

 life cycle at all would reduce male-production, and this has-been 

 the case. 



It may be suggested that our view is very near that of Wliit- 

 ney (14), Mitchell ('13), and Nussbaum ('97), that nutrition 

 is the controlling factor in the Ufe cycle of Hydatina. If nutri- 

 tion be re-defined to include all chemical processes in proto- 



