THE PHENOMKXA OF REVERSIO:^ 



345 



appears dark green, owing to the yellow-ochre ground colour 

 being reduced in extent by the presence of six large green 

 patches. These patches exactly correspond as regards position 

 in the two varieties, and are merely much smaller in A than in 

 B, the sixth spot being wanting in A. Both varieties are repro- 

 duced parthenogenetically in the neighbourhood of Freiburg, and 

 males never appear. 



Fig. 23. — The two varieties of Cy/>ris reptans. 1-6, indicate the six main patches 



of colour on the shell. 



My experiments were made by isolating one female of each 

 variety in a small aquarium, feeding them well, and allowing 

 them to multiply until each vessel was filled with their mature 

 descendants, which in their turn produced eggs. The individuals 

 of the colony were then examined, and the greater number killed 

 and preserved, one or more of them being kept alive and placed 

 separately in fresh aquaria for breeding purposes. 



These animals breed very rapidly throughout the year, and 

 thus in the course of the last eight years many thousands of 

 individuals have passed through my hands. 



The first result obtained by these experiments confirmed 



