386 THE AMEBIC AN NATURALIST [Vol. XLIX 



extreme condition not only do the pigment bands totally 

 disappear, but even the lines between the metameres are 

 broken up, and the location of the external genitalia may 

 be shifted to a more terminal position. All stages exist 

 between this extreme modification and a condition that 

 can not be distinguished from the normal. Owing to 

 this wide range of variability the study of the inher- 

 itance was very difficult until it was found that the reali- 

 zation of the type is a function of the environment. 



In the more extreme types the abdomen is deformed to 

 such an extent that copulation is difficult or impossible. 

 The sterility caused in this way helped also to make the 

 work burdensome, especially when breeding was made 

 with pairs. Instead of pairs, cultures of ten to twenty 

 individuals of the more extreme type were resorted to, 

 as a rule insuring the successful mating of some indi- 

 viduals. Aside from this mechanical difficulty in mating, 

 the mutant race is quite vigorous and of good size. 



